Pregnancy

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June 19, 2009

Methods

Posted by sezaz under Pregnancy - prevention
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Methods

[edit]Physical methods

Physical methods may work in a variety of ways, among them: physically preventing sperm from entering the female reproductive tract; hormonally preventing ovulation from occurring; making the woman’s reproductive tract inhospitable to sperm; or surgically altering the male or female reproductive tract to induce sterility. Some methods use more than one mechanism. Physical methods vary in simplicity, convenience and efficacy.

[edit]Barrier methods

Condom (rolled-up).

Barrier methods place a physical impediment to the movement of sperm into the female reproductive tract.

The most popular barrier method is the male condom, a latex or polyurethane sheath placed over the penis. The condom is also available in a female version, which is made of polyurethane. The female condom has a flexible ring at each end — one secures behind the pubic bone to hold the condom in place, while the other ring stays outside the vagina.

Cervical barriers are devices that are contained completely within the vagina. The contraceptive sponge has a depression to hold it in place over thecervix. The cervical cap is the smallest cervical barrier. Depending on the type of cap, it stays in place by suction to the cervix or to the vaginal walls. The diaphragm fits into place behind the woman’s pubic bone and has a firm but flexible ring, which helps it press against the vaginal walls.

Spermicide may be placed in the vagina before intercourse and creates a chemical barrier. Spermicide may be used alone, or in combination with a physical barrier.

[edit]Hormonal methods

Ortho Tri-cyclen, a brand of oral contraceptive, in a dial dispenser.

There are variety of delivery methods for hormonal contraception.

Oral hormonal contraception was the invention of Carl Djerassi together with Mexican Luis E. Miramontes and Hungarian George Rosenkranz in 1951. The synthesys of norethindrone, a progestin-analogue became part of the first successful oral contraceptive, the combined oral contraceptive pill (COCP). COCPs became known colloquially as the birth-control pill, or simply, the Pill.

Forms of synthetic oestrogens and progestins (synthetic progestogens) combinations commonly used include the combined oral contraceptive pill (“The Pill”), the Patch, and the contraceptive vaginal ring (“NuvaRing”). Not currently available for sale in the United States is Lunelle, a monthly injection.

Other methods contain only a progestin (a synthetic progestogen). These include the progesterone only pill (the POP or ‘minipill’), the injectablesDepo Provera (a depot formulation of medroxyprogesterone acetate given as an intramuscular injection every three months) and Noristerat (Norethindrone acetate given as an intramuscular injection every 8 weeks), and contraceptive implants. The progestin-only pill must be taken at more precisely remembered times each day than combined pills. The first contraceptive implant, the original 6-capsule Norplant, was removed from the market in the United States in 1999, though a newer single-rod implant called Implanon was approved for sale in the United States onJuly 17, 2006. The various progestin-only methods may cause irregular bleeding during use.

[edit]Ormeloxifene (Centchroman)

Ormeloxifene (Centchroman) is a selective estrogen receptor modulator, or SERM. It causes ovulation to occur asynchronously with the formation of the uterine lining, preventing implantation of a zygote. It has been widely available as a birth control method in India since the early 1990s, marketed under the trade name Saheli. Centchroman is legally available only in India.[citation needed]

[edit]Emergency contraception

Some combined pills and POPs may be taken in high doses to prevent pregnancy after a birth control failure (such as a condom breaking) or after unprotected sex. Hormonal emergency contraception is also known as the “morning after pill,” although it is licensed for use up to three days after intercourse.

Copper intrauterine devices may also be used as emergency contraception. For this use, they must be inserted within five days of the birth control failure or unprotected intercourse.

Emergency contraception appears to work by suppressing ovulation.[15][16] However, because it might prevent a fertilized egg from implanting[17], some people[who?] consider it a form of abortion. The details of the possible methods of action are still being studied.

[edit]Intrauterine methods

An intrauterine device.

These are contraceptive devices which are placed inside the uterus. They are usually shaped like a “T” — the arms of the T hold the device in place. There are two main types of intrauterine contraceptives: those that contain copper (which has a spermicidal effect), and those that release aprogestogen (in the US the term progestin is used).

The terminology used for these devices differs in the United Kingdom and the United States. In the US, all devices which are placed in the uterus to prevent pregnancy are referred to as intrauterine devices (IUDs) or intrauterine contraceptive devices (IUCDs). In the UK, only copper-containing devices are called IUDs (or IUCDs), and hormonal intrauterine contraceptives are referred to with the term Intra-Uterine System (IUS). This may be because there are ten types of copper IUDs available in the UK,[18] compared to only one in the US.[19]

[edit]Sterilization

Surgical sterilization is available in the form of tubal ligation for women and vasectomy for men. In women, the process may be referred to as “tying the tubes,” but the fallopian tubes may be tied, cut, clamped, or blocked. This serves to prevent sperm from joining the unfertilized egg. The non-surgical sterilization procedure, Essure, is an example of a procedure that blocks the tubes. Sterilization should be considered permanent.

Although tubal ligation has been known to be permanent they have created the tubal ligation reversal, which in this case is to reverse the procedure to once again have children but also it depends on the kind of tubal ligation procedure that was once done, also depending on the womens age and damage done to the tubes.Tubal Ligation Reversal

[edit]Behavioral methods

Behavioral methods involve regulating the timing or methods of intercourse to prevent the introduction of sperm into the female reproductive tract, either altogether or when an egg may be present.

[edit]Fertility awareness

Symptoms-based methods of fertility awareness involve a woman’s observation and charting of her body’s fertility signs, to determine the fertile and infertile phases of her cycle. Charting may be done by hand or with the assistance of software. Most methods track one or more of the three primary fertility signs:[20] changes in basal body temperature, in cervical mucus, and in cervical position. If a woman tracks both basal body temperature and another primary sign, the method is referred to as symptothermal. Other bodily cues such as mittelschmerz are considered secondary indicators.

Fertility monitors are computerized devices that determine fertility or infertility based on, for example, temperature or urinalysis tests. Calendar-based methods such as the rhythm method and Standard Days Method estimate the likelihood of fertility based on the length of past menstrual cycles. To avoid pregnancy with fertility awareness, unprotected sex is restricted to the least fertile period. During the most fertile period, barrier methods may be availed, or she may abstain from intercourse.

The term natural family planning (NFP) is sometimes used to refer to any use of FA methods. However, this term specifically refers to the practices which are permitted by the Roman Catholic Church — breastfeeding infertility, and periodic abstinence during fertile times. FA methods may be used by NFP users to identify these fertile times.

[edit]Coitus interruptus

Coitus interruptus (literally “interrupted sex”), also known as the withdrawal method, is the practice of ending sexual intercourse (“pulling out”) before ejaculation. The main risk of coitus interruptus is that the man may not perform the maneuver correctly, or may not perform the maneuver in a timely manner. Although concern has been raised about the risk of pregnancy from sperm in pre-ejaculate, several small studies[3][4] have failed to find any viable sperm in the fluid.

[edit]Avoiding vaginal intercourse

The risk of pregnancy from non-vaginal sex, such as with anal sex, oral sex, or non-penetrative sex is virtually zero. A very small risk comes from the possibility of semen leaking onto thevulva (with anal sex) or coming into contact with an object, such as a hand, that later contacts the vulva. Some people maintain complete sexual abstinence to avoid pregnancy.

Although there is no risk of pregnancy from non-vaginal sex which in this case would be anal sex, oral sex, or non-penetrative sex, anal sex is the #1 method of spreading most STD’s- AIDS, Herpes, genital warts, etc. Presenting it as the #1 method is not necessarilly meaning that its the most common way, but it does create the best situation for transmission. It creates this type of transmission because of the likelihood of tearing skin and tissue when you have anal sex.[21]

[edit]Lactational

Most breastfeeding women have a period of infertility after the birth of their child. The lactational amenorrhea method, or LAM, gives guidelines for determining the length of a woman’s period of breastfeeding infertility.

[edit]Induced abortion

This section requires expansion.

In some areas, women use abortion as a primary means to control birth. This practice is more common in Russia,[22] Turkey,[23] and Ukraine.[24] On the other hand, women from Canada[25], and other places[citation needed] generally do not use abortion as a primary form of birth control. Abortion is subject to ethical debate.

Surgical abortion methods include suction-aspiration abortion (used in the first trimester) or dilation and evacuation (used in the second trimester). Medical abortion methods involve the use of medication which is swallowed or inserted vaginally to induce abortion. Medical abortion can be used if the length of gestation has not exceeded 8 weeks.

Some herbs are considered abortifacient, and some animal studies have found various herbs to be effective in inducing abortion in non-human animal species.[7][26] Humans generally do not use herbs when other methods are available, due to the unknown efficacy and due to risks of toxicity.

[edit]Methods in development

[edit]For females

Praneem is a polyherbal vaginal tablet being studied as a spermicide, and a microbicide active against HIV.[27]
BufferGel is a spermicidal gel being studied as a microbicide active against HIV.[28]
Duet is a disposable diaphragm in development that will be pre-filled with BufferGel.[29] It is designed to deliver microbicide to both the cervix and vagina. Unlike currently available diaphragms, the Duet will be manufactured in only one size and will not require a prescription, fitting, or a visit to a doctor.[28]
The SILCS diaphragm is a silicone barrier which is still in clinical testing. It has a finger cup molded on one end for easy removal. Like the Duet, the SILCS is novel in that it will only be available in one size.
A vaginal ring is being developed that releases both estrogen and progesterone, and is effective for over 12 months.[30]
Two types of progestogen-only vaginal rings are being developed. Progestogen-only products may be particularly useful for women who are breastfeeding.[30] The rings may be used for four months at a time.[31]
A progesterone-only contraceptive is being developed that would be sprayed onto the skin once a day.[32]
Quinacrine sterilization and the Adiana procedure are two permanent methods of birth control being developed.[33]

[edit]For males

Main article: Male contraceptive

Other than condoms and withdrawal, there are currently no available methods of reversible contraception which males can use or control. Several methods are in research and development:

As of 2007, a chemical called Adjudin is currently in Phase II human trials as a male oral contraceptive.[34]

RISUG (Reversible Inhibition of Sperm Under Guidance), is an experimental injection into the vas deferens that coats the walls of the vas with a spermicidal substance. The method can potentially be reversed by washing out the vas deferens with a second injection.

Experiments in vas-occlusive contraception involve an implant placed in the vasa deferentia.

Experiments in heat-based contraception involve heating a man’s testicles to a high temperature for a short period of time.

[edit]Misconceptions

Modern misconceptions and urban legends have given rise to a great many false claims:

The suggestion that douching with any substance immediately following intercourse works as a contraceptive is untrue. While it may seem like a sensible idea to try to wash the ejaculate out of the vagina, it is not likely to be effective. Due to the nature of the fluids and the structure of the female reproductive tract, douching most likely actually spreads semen further towards the uterus. Some slight spermicidal effect may occur if the douche solution is particularly acidic, but overall it is not scientifically observed to be a reliably effective method. Douching is neither a contraceptive, or preventatives measure against STDs or other infections.

Vaginal Douching

It is untrue that a female cannot become pregnant as a result of the first time she engages in sexual intercourse.
While women are usually less fertile for the first few days of menstruation,[35] it is a myth that a woman absolutely cannot get pregnant if she has sex during her period.
Having sex in a hot tub does not prevent pregnancy, but may contribute to vaginal infections.[36]
Although some sex positions may encourage pregnancy, no sexual positions prevent pregnancy. Having sex while standing up or with a woman on top will not keep the sperm from entering the uterus. The force of ejaculation, the contractions of the uterus caused by prostaglandins[citation needed] in the semen, as well as ability of sperm to swim overrides gravity.
Urinating after sex does not prevent pregnancy and is not a form of birth control, although it is often advised anyway to help prevent urinary tract infections.[37]
Toothpaste cannot be used as an effective contraceptive[38].

[edit]Effectiveness

See also the table at: Comparison of birth control methods

Effectiveness is measured by how many women become pregnant using a particular birth control method in the first year of use. Thus, if 100 women use a method that has a 12 percent first-year failure rate, then sometime during the first year of use, 12 of the women should become pregnant.

The most effective methods in typical use are those that do not depend upon regular user action. Surgical sterilization, Depo-Provera, implants, and intrauterine devices (IUDs) all have first-year failure rates of less than one percent for perfect use. Sterilization, implants, and IUDs also have typical failure rates under one percent. The typical failure rate of Depo-Provera is disagreed upon, with figures ranging from less than one percent up to three percent.[39][40]

Other methods may be highly effective if used consistently and correctly, but can have typical use first-year failure rates that are considerably higher due to incorrect or ineffective usage by the user. Hormonal contraceptive pills, patches or rings, fertility awareness methods, and the lactational amenorrhea method (LAM), if used strictly, have first-year (or for LAM, first-6-month) failure rates of less than 1%.[41][42][43][44] In one survey, typical use first-year failure rates of hormonal contraceptive pills (and by extrapolation, patches or rings) were as high as five percent per year. Fertility awareness methods as a whole have typical use first-year failure rates as high as 25 percent per year; however, as stated above, perfect use of these methods reduces the first-year failure rate to less than 1%.[39]

Condoms and cervical barriers such as the diaphragm have similar typical use first-year failure rates (14 and 20 percent, respectively), but perfect usage of the condom is more effective (three percent first-year failure vs six percent) and condoms have the additional feature of helping to prevent the spread of sexually transmitted diseases such as the HIV virus. The withdrawal method, if used consistently and correctly, has a first-year failure rate of four percent. Due to the difficulty of consistently using withdrawal correctly, it has a typical use first-year failure rate of 19 percent,[39] and is not recommended by some medical professionals.[45]

[edit]Protection against sexually transmitted infections

See also: Safe sex

Some methods of birth control also offer protection against sexually transmitted infections (STIs). The male latex condom offers some protection against some STIs with correct and consistent use, as does the female condom, although the latter has only been approved for vaginal sex. The female condom may offer greater protection against STIs that pass through skin to skin contact, as the outer ring covers more exposed skin than the male condom. Some of the methods involved in avoiding vaginal intercourse can also reduce risk: latex or polyurethane barriers can be used during oral sex, and mutual or solo masturbation are very low-risk. The remaining methods of birth control do not offer significant protection against the sexual transmission of STIs.

Even though the female condom may offer greater protection against STIs, there can still be a possibility that you can transmit an infection. Mainly because some of these STIs like herpes are transmitted through skin to skin contact especially through periods of asymptomatic shedding. These female condoms or other methods of birth control only reduces the risk rather than eliminating it. [46]

Many STIs may also be transmitted non-sexually; this is one reason why abstinence from sexual behavior does not guarantee 100 percent protection against sexually transmitted infections. For example, HIV may be transmitted through contaminated needles which may be used in intravenous drug use, tattooing, body piercing, or injections. Health-care workers have acquired HIV through occupational exposure to accidental injuries with needles.[47]

[edit]Religious and cultural attitudes

[edit]Religious views on birth control

Main article: Religious views on birth control

Religions vary widely in their views of the ethics of birth control. In Christianity, the Roman Catholic Church accepts only Natural Family Planning,[48] while Protestants maintain a wide range of views from allowing none to very lenient.[49] Views in Judaism range from the stricter Orthodox sect to the more relaxed Reform sect.[50] In Islam, contraceptives are allowed if they do not threaten health or lead to sterility, although their use is discouraged.[51] Hindus may use both natural and artificial contraceptives.[52] A common Buddhist view of birth control is that preventing conception is ethically acceptable, while intervening after conception has occurred or may have occurred is not.[53]

[edit]Birth control education

Many teenagers, most commonly in developed countries, receive some form of sex education in school. What information should be provided in such programs is hotly contested, especially in the United States and United Kingdom. Possible topics include reproductive anatomy, human sexual behavior, information on sexually transmitted diseases (STDs), social aspects of sexual interaction, negotiating skills intended to help teens follow through with a decision to remain abstinent or to use birth control during sex, and information on birth control methods.

One type of sex education program used mainly in the United States is called abstinence-only education, and it promotes complete sexual abstinence until marriage. The programs do not encourage birth control, often provide inaccurate information about contraceptives and sexuality[54], stress failure rates of condoms and other contraceptives, and teach strategies for avoiding sexually intimate situations. Advocates of abstinence-only education believe that the programs will result in decreased rates of teenage pregnancy and STD infection. In a non-random, Internet survey of 1,400 women who found and completed a 10-minute multiple-choice online questionnaire listed in one of several popular search engines, women who received sex education from schools providing primarily abstinence information, or contraception and abstinence information equally, reported fewer unplanned pregnancies than those who received primarily contraceptive information, who in turn reported fewer unplanned pregnancies than those who received no information.[55] However, randomized controlled trials demonstrate that abstinence-only sex education programs increase the rates of pregnancy and STDs in the teenage population.[56][57] Professional medical organizations, including the AMA, AAP, ACOG,APHA, APA–Mnd marquez (talk) 11:04, 17 June 2009 (UTC),and Society for Adolescent Medicine, support comprehensive sex education (providing abstinence and contraceptive information) and oppose the sole use of abstinence-only sex education.[58][59]

June 19, 2009

Birth control – introduction

Posted by sezaz under Pregnancy - prevention
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From Wikipedia, the free encyclopedia

(Redirected from Pregnancy prevention)

It has been suggested that some content from this article or section be split into a separate article entitled Contraception. (Discuss)

For other uses, see Birth control (disambiguation).

A family planning centre in Kuala Terengganu,Malaysia.

Birth control is a regimen of one or more actions, devices, or medications followed in order to deliberately prevent or reduce the likelihood of pregnancy or childbirth.^{[citation needed]} There are three main routes to preventing or ending pregnancy; the prevention of fertilization of theovum by sperm cells (“contraception“), the prevention of implantation of the blastocyst (“contragestion“), and the chemical or surgical induction of abortion of the developing embryo or, later, fetus. In common usage, term “contraception” is often used for both contraception and contragestion.

Birth control is commonly used as part of family planning.

The history of birth control began with the discovery of the connection between coitus and pregnancy. The oldest forms of birth control included coitus interruptus, pessaries, and the ingestion of herbs that were believed to be contraceptive or abortifacient. The earliest record of birth control use is an ancient Egyptian set of instructions on creating a contraceptive pessary.

Different methods of birth control have varying characteristics. Condoms, for example, are the only methods that provide significant protection from sexually transmitted diseases. Cultural and religious attitudes on birth control vary significantly.

[edit]History

“And the villain still pursues her.” Satirical Victorian era postcard.

Probably the oldest methods of contraception (aside from avoiding vaginal intercourse) are coitus interruptus, lactational, certain barrier methods, and herbal methods (emmenagogues and abortifacients).

In Germany, during the reign of Hitler, and before World War II, in 1935, birth control information was readily available to outcast groups including Jews, Gypsies, Slavs, and mentally or physically disabled people. When it came to women that were classified as Aryan, they were forbidden to receive information after the Nuremberg Laws were implemented. In Russia to faciliate social equality between men and women, Russia made birth control readily available. Aleksandra Kollontai (1872-1952), was the commissar for public welfare during this time, promoted birth control education for adults as well. When it came to birth control in France, women were working for reproductive rights and they helped end the nation’s ban on birth control in 1965. Finally in 1970, in Catholic Italy, feminists won the right to gain access to birth control information.^[1]

Much earlier than this, satirical English author Daniel Defoe wrote Conjugal Lewdness. The full original title of this 1727 essay was “Conjugal Lewdness or, Matrimonial Whoredom”, though he was later asked to rename it for the sake of propriety. The modified title became “A Treatise Concerning the Use and Abuse of the Marriage Bed”. The essay dealt primarily with contraception, comparing it directly with infanticide. Defoe accomplished this through anecdotes, such as a conversation between two women in which the right-minded chides the other for asking for “recipes” that might prevent pregnancy. In the essay, he further referred to contraception as “the diabolical practice of attempting to prevent childbearing by physical preparations.”

Coitus interruptus (withdrawal of the penis from the vagina prior to ejaculation) probably predates any other form of birth control. This is not a particularly reliable method of contraception, as few men have the self-control to correctly practice the method at every single act of sexual intercourse.^[2] Although it is commonly believed that pre-ejaculate fluid can cause pregnancy, modern research has shown that pre-ejaculate fluid does not contain viable sperm.^[3]^[4]

There are historic records of Egyptian women using a pessary (a vaginal suppository) made of various acidic substances and lubricated with honey or oil, which may have been somewhat effective at killing sperm.^[5] However, it is important to note that the sperm cell was not discovered until Anton van Leeuwenhoek invented the microscope in the late 17th century, so barrier methods employed prior to that time could not know of the details of conception. Asian women may have used oiled paper as a cervical cap, and Europeans may have used beeswax for this purpose. The condom appeared sometime in the 17th century, initially made of a length of animal intestine. It was not particularly popular, nor as effective as modern latex condoms, but was employed both as a means of contraception and in the hopes of avoiding syphilis, which was greatly feared and devastating prior to the discovery of antibiotic drugs.

Various abortifacients have been used throughout human history in attempts to terminate undesired pregnancy. Some of them were effective, some were not; those that were most effective also had major side effects. One abortifacient reported to have low levels of side effects—silphium—was harvested to extinction around the 1st century.^[6] The ingestion of certain poisonsby the female can disrupt the reproductive system; women have drunk solutions containing mercury, arsenic, or other toxic substances for this purpose. The Greek gynaecologist Soranusin the 2nd century suggested that women drink water that blacksmiths had used to cool metal. The herbs tansy and pennyroyal are well-known in folklore as abortive agents, but these also “work” by poisoning the woman. Levels of the active chemicals in these herbs that will induce a miscarriage are high enough to perilously damage the liver, kidneys, and other organs. However, in those times where risk of maternal death from postpartum complications was high, the risks and side effects of toxic medicines may have seemed less onerous. Someherbalists claim that black cohosh tea will also be effective in certain cases as an abortifacient.^[7]

Aside from abortifacients, herbal contraceptives in folklore have also included a few preventative measures. Hibiscus rosa-sinensis, known in Ayurveda as a contraceptive, may have antiestrogenic properties.^[8] Papaya seeds, rumored to be a male contraceptive, have recently been studied for their azoospermic effect on monkeys.^[9]

During the medieval period, physicians in the Islamic world listed many birth control substances in their medical encyclopedias. Avicenna listing 20 in The Canon of Medicine (1025) andMuhammad ibn Zakariya ar-Razi listing 176 in his Hawi (10th century). This was unparalleled in European medicine until the 19th century.^[10]

The fact that various effective methods of birth control were known in the ancient world sharply contrasts with a seeming ignorance of these methods in wide segments of the population of early modern Christian Europe. This ignorance continued far into the 20th century, and was paralleled by eminently high birth rates in European countries during the 18th and 19th centuries.^[11] Some historians have attributed this to a series of coercive measures enacted by the emerging modern state, in an effort to repopulate Europe after the population catastrophe of the Black Death, starting in 1348. According to this view, the witch hunts were the first measure the modern state took in an attempt to eliminate knowledge about birth control within the population, and monopolize it in the hands of state-employed male medical specialists (gynecologists). Prior to the witch hunts, male specialists were unheard of, because birth control was naturally a female domain.^[12]

Presenters at a family planning conference told a tale of Arab traders inserting small stones into the uteruses of their camels in order to prevent pregnancy, a concept very similar to the modern IUD. Although the story has been repeated as truth, it has no basis in history and was meant only for entertainment purposes.^[13] The first interuterine devices (which occupied both the vagina and the uterus) were first marketed around 1900. The first modern intrauterine device (contained entirely in the uterus) was described in a German publication in 1909. TheGräfenberg ring, the first IUD that was used by a significant number of women, was introduced in 1928.^[14]

The rhythm method (with a rather high method failure rate of ten percent per year)^{[citation needed]} was developed in the early 20th century, as researchers discovered that a woman only ovulates once per menstrual cycle. Not until the 1950s, when scientists better understood the functioning of the menstrual cycle and the hormones that controlled it, were methods ofhormonal contraception and modern methods of fertility awareness (also called natural family planning) developed.

Margaret Sanger was an American birth control activist and the founder of the American Birth Control League (which eventually became Planned Parenthood). She was instrumental in opening the way to access birth control.

In 1960 the FDA approved the first form of hormonal birth control, the combined oral contraceptive pill.

May 27, 2009

Pregnancy

Posted by sezaz under About pregnancy
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Pregnancy

From Wikipedia, the free encyclopedia

This article is about pregnancy in female humans. For pregnancy in non-human animals, see Gestation. For pregnancy in males, see Male pregnancy.

A pregnant woman near the end of her term

Pregnancy Classification and external resources
ICD-9	V22

Pregnancy (latin graviditas) is the carrying of one or more offspring, known as a fetus or embryo, inside the uterus of a female. In a pregnancy, there can be multiple gestations, as in the case of twins or triplets. Human pregnancy is the most studied of all mammalian pregnancies. Obstetrics is the surgical field that studies and cares for high risk pregnancy. Midwifery is the non-surgical field that cares for pregnancy and pregnant women.

Childbirth usually occurs about 38 weeks after conception, i.e., approximately 40 weeks from the last normal menstrual period (LNMP) in humans. The World Health Organization defines normal term for delivery as between 37 weeks and 42 weeks. The calculation of this date involves the assumption of a regular 28-day period.

[edit]Terminology

One scientific term for the state of pregnancy is gravid, and a pregnant female is sometimes referred to as a gravida.^[1] Neither word is used in common speech. Similarly, the term “parity” (abbreviated as “para”) is used for the number of previous successful live births. Medically, a woman who has never been pregnant is referred to as a “nulligravida”, and in subsequent pregnancies as “multigravida” or “multiparous”.^[2]^[3]^[4] Hence, during a second pregnancy a woman would be described as “gravida 2, para 1″ and upon delivery as “gravida 2, para 2.” An in-progress pregnancy, as well as abortions, miscarriages, or stillbirths account for parity values being less than the gravida number, whereas a multiple birth will increase the parity value. Women who have never carried a pregnancy achieving more than 20 weeks of gestation age are referred to as “nulliparous”.^[5] The medical term for a woman who is pregnant for the first time is primigravida.^[6]

The term embryo is used to describe the developing offspring during the first 8 weeks following conception, and the term fetus is used from about 2 months of development until birth.^[7]^[8]

In many societies’ medical or legal definitions, human pregnancy is somewhat arbitrarily divided into three trimester periods, as a means to simplify reference to the different stages ofprenatal development. The first trimester carries the highest risk of miscarriage (natural death of embryo or fetus). During the second trimester, the development of the fetus can be more easily monitored and diagnosed. The beginning of the third trimester often approximates the point of viability, or the ability of the fetus to survive, with or without medical help, outside of theuterus.^[9]

[edit]Progression

Stages in prenatal development, with weeks and months numbered by gestation.

[edit]Initiation

Pregnancy occurs as the result of the female gamete or oocyte being penetrated by the male gamete, spermatozoon, in a process referred to, in medicine, as “fertilization,” or more commonly known as “conception.” After the point of “fertilization,” it is referred to as an egg. The fusion of male and female gametes usually occurs through the act of sexual intercourse. However, the advent of artificial insemination and in vitro fertilisation have also made achieving pregnancy possible in cases where sexual intercourse does not result in fertilization (e.g., through choice or male/female infertility).

[edit]Perinatal period

Perinatal defines the period occurring “around the time of birth“, specifically from 22 completed weeks (154 days) of gestation (the time when birth weight is normally 500 g) to 7 completed days after birth. ^[10]

Legal regulations in different countries include gestation age beginning from 16 to 22 weeks (5 months) before birth.

[edit]Postnatal period

Main article: Postnatal

[edit]Duration

The expected date of delivery (EDD) is 40 weeks counting from the last menstrual period (LMP), and birth usually occurs between 37 and 42 weeks.^[11] The actual pregnancy duration is typically 38 weeks after conception. Though pregnancy begins at conception, it is more convenient to date from the first day of a woman’s last menstrual period, or from the date of conception if known. Starting from one of these dates, the expected date of delivery can be calculated. Forty weeks is 9 months and 6 days, which forms the basis of Naegele’s rule for estimating date of delivery. More accurate and sophisticated algorithms take into account other variables, such as whether this is the first or subsequent child (i.e., pregnant woman is a primip or a multip, respectively), ethnicity, parental age, length of menstrual cycle, and menstrual regularity.

Pregnancy is considered “at term” when gestation attains 37 complete weeks but is less than 42 (between 259 and 294 days since LMP). Events before completion of 37 weeks (259 days) are considered preterm; from week 42 (294 days) events are considered postterm.^[12] When a pregnancy exceeds 42 weeks (294 days), the risk of complications for woman and fetus increases significantly.^[11]^[13] As such, obstetricians usually prefer to induce labour, in an uncomplicated pregnancy, at some stage between 41 and 42 weeks.^[14]^[15]

Recent medical literature prefers the terminology preterm and postterm to premature and postmature. Preterm and postterm are unambiguously defined as above, whereas premature andpostmature have historical meaning and relate more to the infant’s size and state of development rather than to the stage of pregnancy.^[16]^[17]

Fewer than 5% of births occur on the due date; 50% of births are within a week of the due date, and almost 90% within 2 weeks.^[18] It is much more useful, therefore, to consider a range of due dates, rather than one specific day, with some online due date calculators providing this information.

Accurate dating of pregnancy is important, because it is used in calculating the results of various prenatal tests (for example, in the triple test). A decision may be made to induce labour if a fetus is perceived to be overdue. Furthermore, if LMP and ultrasound dating predict different respective due dates, with the latter being later, this might signify slowed fetal growth and therefore require closer review.

The Age of Viability has been receding relentlessly as medical revolution continues to unfold. Whereas it used to be 28 weeks, this has been brought back to as early as 23 weeks [22 weeks in a few countries]. Unfortunately, there has been a profound increase in morbidity and mortality associated with the increased survival to the extent it has led some to question theethics and morality of resuscitating at the edge of viability.

[edit]Childbirth

Main article: Childbirth

Childbirth is the process whereby an infant is born. It is considered by many to be the beginning of a person’s life, and age is defined relative to this event in most cultures.

A woman is considered to be in labour when she begins experiencing regular uterine contractions, accompanied by changes of her cervix — primarily effacement and dilation. While childbirth is widely experienced as painful, some women do report painless labours, while others find that concentrating on the birth helps to quicken labour and lessen the sensations. Most births are successful vaginal births, but sometimes complications arise and a woman may undergo a cesarean section.

During the time immediately after birth, both the mother and the baby are hormonally cued to bond, the mother through the release of oxytocin, a hormone also released duringbreastfeeding.

[edit]Diagnosis

Main article: Obstetrics

The beginning of pregnancy may be detected in a number of different ways, either by a pregnant woman without medical testing, or by using medical tests with or without the assistance of a medical professional.

Most pregnant women experience a number of symptoms, which can signify pregnancy. The symptoms can include nausea and vomiting, excessive tiredness and fatigue, craving for certain foods not normally considered a favorite, and frequent urination particularly during night.

A number of early medical signs are associated with pregnancy.^[19]^[20] These signs typically appear, if at all, within the first few weeks after conception. Although not all of these signs are universally present, nor are all of them diagnostic by themselves, taken together they make a presumptive diagnosis of pregnancy. These signs include the presence of human chorionic gonadotropin (hCG) in the blood and urine, missed menstrual period, implantation bleeding that occurs at implantation of the embryo in the uterus during the third or fourth week after last menstrual period, increased basal body temperature sustained for over 2 weeks after ovulation, Chadwick’s sign (darkening of the cervix, vagina, and vulva), Goodell’s sign (softening of the vaginal portion of the cervix), Hegar’s sign (softening of the uterus isthmus), and pigmentation of linea alba - Linea nigra, (darkening of the skin in a midline of the abdomen, caused byhyperpigmentation resulting from hormonal changes, usually appearing around the middle of pregnancy).^[19]^[20]

Pregnancy detection can be accomplished using one or more of various pregnancy tests, which detect hormones generated by the newly formed placenta. Clinical blood and urine tests can detect pregnancy soon after implantation, which is as early as 6 to 8 days after fertilization. Blood pregnancy tests are more accurate than urine tests.^[21] Home pregnancy tests are personal urine tests, which normally cannot detect a pregnancy until at least 12 to 15 days after fertilization. Both clinical and home tests can only detect the state of pregnancy, and cannot detect the age of the embryo.

In the post-implantation phase, the blastocyst secretes a hormone named human chorionic gonadotropin, which in turn stimulates the corpus luteum in the woman’s ovary to continue producing progesterone. This acts to maintain the lining of the uterus so that the embryo will continue to be nourished. The glands in the lining of the uterus will swell in response to the blastocyst, and capillaries will be stimulated to grow in that region. This allows the blastocyst to receive vital nutrients from the woman.

Despite all the signs, some women may not realize they are pregnant until they are quite far along in their pregnancy, in some cases not even until they begin labour. This can be caused by many factors, including irregular periods (quite common in teenagers), certain medications (not related to conceiving children), and obese women who disregard their weight gain. Others may be in denial of their situation.

An early sonograph can determine the age of the pregnancy fairly accurately. In practice, doctors typically express the age of a pregnancy (i.e., an “age” for an embryo) in terms of “menstrual date” based on the first day of a woman’s last menstrual period, as the woman reports it. Unless a woman’s recent sexual activity has been limited, or she has been charting her cycles, or the conception is as the result of some types of fertility treatment (such as IUI or IVF) the exact date of fertilization is unknown. Absent symptoms such as morning sickness, often the only visible sign of a pregnancy is an interruption of her normal monthly menstruation cycle, (i.e., a “late period”). Hence, the “menstrual date” is simply a common educated estimate for the age of a fetus, which is an average of 2 weeks later than the first day of the woman’s last menstrual period. The term “conception date” may sometimes be used when that date is more certain, though even medical professionals can be imprecise with their use of the two distinct terms. The due date can be calculated by using Naegele’s rule. The expected date of delivery may also be calculated from sonogram measurement of the fetus. This method is slightly more accurate than methods based on LMP.^[22] The beginning of labour, which is variously called confinement or childbed, begins on the day predicted by LMP 3.6% of the time and on the day predicted by sonography 4.3% of the time.^[23]

Diagnostic criteria are: Women who have menstrual cycles and are sexually active, a period delayed by a few days or weeks is suggestive of pregnancy; elevated B-hcG to around 100,000 mIU/mL by 10 weeks of gestation.^[1]

[edit]Physiology

The term trimester redirects here. For the term trimester used in academic settings, see Academic term

Pregnancy is typically broken into three periods, or trimesters, each of about three months. While there are no hard and fast rules, these distinctions are useful in describing the changes that take place over time.

[edit]First trimester

Comparison of growth of the abdomen between 26 weeks and 40 weeks gestation.

Traditionally, doctors have measured pregnancy from a number of convenient points, including the day of last menstruation, ovulation, fertilization, implantation and chemical detection. In medicine, pregnancy is often defined as beginning when the developing embryo becomes implanted into theendometrial lining of a woman’s uterus. In some cases where complications may have arisen, the fertilized egg might implant itself in the fallopian tubesor the cervix, causing an ectopic pregnancy. Most pregnant women do not have any specific signs or symptoms of implantation, although it is not uncommon to experience minimal bleeding at implantation. Some women will also experience cramping during their first trimester. This is usually of no concern unless there is spotting or bleeding as well. After implantation the uterine endometrium is called the decidua.The placenta which is formed partly from the decidua and partly from outer layers of the embryo is responsible for transport of nutrients and oxygen to, and removal of waste products from the fetus. The umbilical cord is the connecting cord from the embryo or fetus to the placenta.The developing embryo undergoes tremendous growth and changes during the process of fetal development.

Morning sickness can occur in about seventy percent of all pregnant women and typically improves after the first trimester.^[24]

In the first 12 weeks of pregnancy the nipples and areolas darken due to a temporary increase in hormones. ^[25]

Most miscarriages occur during this period.

A pregnant woman at 26 weeks

[edit]Second trimester

Months 4 through 6 of the pregnancy are called the second trimester. Most women feel more energized in this period, and begin to put on weight as the symptoms of morning sickness subside and eventually fade away.

In the 20th week the uterus, the muscular organ that holds the developing fetus, can expand up to 20 times its normal size during pregnancy. Although the fetus begins moving and takes a recognizable human shape during the first trimester, it is not until the second trimester that movement of the fetus, often referred to as “quickening“, can be felt. This typically happens in the fourth month, more specifically in the 20 to 21 week, or by the 19th week if the woman has been pregnant before. However, it is not uncommon for some women to not feel the fetus move until much later. The placenta is now fully functioning and the fetus is making insulin and urinating. The reproductive organs distinguish the fetus as male or female.

[edit]Third trimester

Final weight gain takes place, which is the most weight gain throughout the pregnancy. The fetus will be growing the most rapidly during this stage, gaining up to 28g per day. The woman’s belly will transform in shape as the belly drops due to the fetus turning in a downward position ready for birth. During the second trimester, the woman’s belly would have been very upright, whereas in the third trimester it will drop down quite low, and the woman will be able to lift her belly up and down. The fetus begins to move regularly, and is felt by the woman. Fetal movement can become quite strong and be disruptive to the woman. The woman’s navel will sometimes become convex, “popping” out, due to her expanding abdomen. This period of her pregnancy can be uncomfortable, causing symptoms like weak bladder control and back-ache. Movement of the fetus becomes stronger and more frequent and via improved brain, eye, and muscle function the fetus is prepared for ex utero viability. The woman can feel the fetus “rolling” and it may cause pain or discomfort when it is near the woman’s ribs and spine.

It is during this time that a baby born prematurely may survive. The use of modern medical intensive care technology has greatly increased the probability of premature babies surviving, and has pushed back the boundary of viability to much earlier dates than would be possible without assistance.^[26] In spite of these developments, premature birth remains a major threat to the fetus, and may result in ill-health in later life, even if the baby survives.

[edit]Prenatal development and sonograph images

[edit]Physiological changes in pregnancy

The body must change its physiological and homeostatic mechanisms in pregnancy to ensure the fetus is provided for. Increases in blood sugar, breathing and cardiac output are all required.

[edit]Hormonal changes

Levels of progesterone and oestrogens rise continually throughout pregnancy, suppressing the hypothalamic axis and subsequently the menstrual cycle. The woman and the placenta also produce many hormones.

Prolactin levels increase due to maternal Pituitary gland enlargement by 50%. This mediates a change in the structure of the Mammary gland from ductal to lobular-alveolar. Parathyroid hormone is increased due to increases of calcium uptake in the gut and reabsorption by the kidney. Adrenal hormones such as cortisol and aldosterone also increase.

Placental lactogen is produced by the placenta and stimulates lipolysis and fatty acid metabolism by the woman, conserving blood glucose for use by the fetus. It also decreases maternal tissue sensitivity to insulin, resulting in gestational diabetes.

[edit]Musculoskeletal changes

The body’s posture changes as the pregnancy progresses. The pelvis tilts and the back arches to help keep balance. Poor posture occurs naturally from the stretching of the woman’s abdominal muscles as the fetus grows. These muscles are less able to contract and keep the lower back in proper alignment. The pregnant woman has a different pattern of gait. The step lengthens as the pregnancy progresses, due to weight gain and changes in posture. On average, a woman’s foot can grow by a half size or more during pregnancy. In addition, the increased body weight of pregnancy, fluid retention, and weight gain lowers the arches of the foot, further adding to the foot’s length and width. The influences of increased hormones such as estrogen and relaxin initiate the remodeling of soft tissues, cartilage and ligaments. Certain skeletal joints such as the symphysis pubis and sacroiliac widen or have increased laxity.

[edit]Physical changes

One of the most noticeable alterations in pregnancy is the gain in weight. The enlarging uterus, the growing fetus, the placenta and liquor amnii, the acquisition of fat and water retention, all contribute to this increase in weight. The weight gain varies from person to person and can be anywhere from 5 pounds (2.3 kg) to over 100 pounds (45 kg). In America, the doctor-recommended weight gain range is 25 pounds (11 kg) to 35 pounds (16 kg), less if the woman is overweight, more (up to 40 pounds (18 kg)) if the woman is underweight.

Other physical changes during pregnancy include breasts increasing two cup sizes. Also areas of the body such as the forehead and cheeks (known as the ‘mask of pregnancy’) become darker due to the increase of melanin being produced.^[39]

The female body experiences many changes as the fetus grows through each trimester as shown and discussed in this pregnancy video. Two women at different stages in their pregnancy illustrate what has happened to their bodies.

[edit]Cardiovascular changes

Blood volume increases by 40% in the first two trimesters. This is due to an increase in plasma volume through increased aldosterone. Progesterone may also interact with the aldosterone receptor, thus leading to increased levels. Red blood cell numbers increase due to increased erythropoietin levels.

Cardiac function is also modified, with increase heart rate and increased stroke volume. A decrease in vagal tone and increase in sympathetic tone is the cause. Blood volume increases act to increase stroke volume of the heart via Starling’s law. After pregnancy the change in stroke volume is not reversed. Cardiac output rises from 4 to 7 litres in the 2nd trimester.

Blood pressure also fluctuates. In the first trimester it falls. Initially this is due to decreased sensitivity to angiotensin and vasodilation provoked by increased blood volume. Later, however, it is caused by decreased resistance to the growing uteroplacental bed.

[edit]Respiratory changes

Decreased functional residual capacity is seen, typically falling from 1.7 to 1.35 litres, due to the compression of the diaphragm by the uterus. Tidal volume increases, from 0.45 to 0.65 litres, giving an increase in pulmonary ventilation. This is necessary to meet the increased oxygen requirement of the body, which reaches 50ml/min, 20ml of which goes to reproductive tissues.

Progesterone may act centrally on chemoreceptors to reset the set point to a lower partial pressure of carbon dioxide. This maintains an increased respiration rate even at a decreased level of carbon dioxide.

[edit]Metabolic changes

An increased requirement for nutrients is given by fetal growth and fat deposition. Changes are caused by steroid hormones, lactogen, and cortisol.

Maternal insulin resistance can lead to gestational diabetes. Increase liver metabolism is also seen, with increased gluconeogenesis to increase maternal glucose levels.

[edit]Renal changes

Renal plasma flow increases, as does aldosterone and erthropoietin production as discussed. The tubular maximum for glucose is reduced, which may precipitate gestational diabetes.

[edit]Management

Prenatal medical care is of recognized value throughout the developed world. Periconceptional Folic acid supplementation is the only type of supplementation of proven efficacy.

[edit]Nutrition

Main article: Nutrition and pregnancy

A balanced, nutritious diet is an important aspect of a healthy pregnancy. Eating a healthy diet, balancing carbohydrates, fat, and proteins, and eating a variety of fruits and vegetables, usually ensures good nutrition. Those whose diets are affected by health issues, religious requirements, or ethical beliefs may choose to consult a health professional for specific advice.

Adequate periconceptional folic acid (also called folate or Vitamin B9) intake has been proven to limit fetal neural tube defects, preventing spina bifida, a very serious birth defect. The neural tube develops during the first 28 days of pregnancy, explaining the necessity to guarantee adequate periconceptional folate intake.^[40]^[41] Folates (from folia, leaf) are abundant in spinach(fresh, frozen, or canned), and are also found in green vegetables, salads, citrus fruit and melon, chickpeas (i.e. in the form of hummus or falafel), and eggs. In the United States and Canada, most wheat products (flour, noodles) are fortified with folic acid.^[42]

DHA omega-3 is a major structural fatty acid in the brain and retina, and is naturally found in breast milk. It is important for a mother to consume adequate amounts of DHA during pregnancy and while nursing to support her well-being and the health of her infant. Developing infants cannot produce DHA efficiently, and must receive this vital nutrient from the mother through the placenta during pregnancy and in breast milk after birth.^[43]

Several micronutrients are important for the health of the developing fetus, especially in areas of the world where insufficient nutrition is prevalent.^[44] In developed areas, such as Western Europe and the United States, certain nutrients such as Vitamin D and calcium, required for bone development, may require supplementation.^[45]^[46]^[47]

Dangerous bacteria or parasites may contaminate foods, particularly listeria and toxoplasma, toxoplasmosis agent. Careful washing of fruits and raw vegetables may remove these pathogens, as may thoroughly cooking leftovers, meat, or processed meat. Soft cheeses may contain listeria; if milk is raw the risk may increase. Cat feces pose a particular risk of toxoplasmosis. Pregnant women are also more prone to catching salmonella infections from eggs and poultry, which should be thoroughly cooked. Practicing good hygiene in the kitchen can reduce these risks.^[48]

[edit]Weight gain

Caloric intake must be increased, to ensure proper development of the fetus. The amount of weight gained during pregnancy varies among women. The National Health Service recommends that overall weight gain during the 9 month period for women who start pregnancy with normal weight be 10 to 12 kilograms (22–26 lb).^[49] During pregnancy, insufficient weight gain can compromise the health of the fetus. Women with fears of weight gain or with eating disorders may choose to work with a health professional, to ensure that pregnancy does not trigger disordered eating. Likewise, excessive weight gain can pose risks to the woman and the fetus. Women who are prone to being overweight may choose to plan a healthy diet and exercise to help moderate the amount of weight gained.

[edit]Immunological tolerance

Main article: Pre-eclampsia

Research on the immunological basis for pre-eclampsia has indicated that continued exposure to a partner’s semen has a strong protective effect against pre-eclampsia, largely due to the absorption of several immune modulating factors present in seminal fluid.^[50] Studies also showed that long periods of sexual cohabitation with the same partner fathering a woman’s child significantly decreased her chances of suffering pre-eclampsia.^[51] Several other studies have since investigated the strongly decreased incidence of pre-eclampsia in women who had received blood transfusions from their partner, those with long, preceding histories of sex without barrier contraceptives, and in women who had been regularly performing oral sex,^[52] with one study concluding that “induction of allogeneic tolerance to the paternal HLA molecules of the fetus may be crucial. Data collected strongly suggests that exposure, and especially oral exposure to soluble HLA from semen can lead to transplantation tolerance.”^[52]

Other studies have investigated the roles of semen in the female reproductive tracts of mice, showing that “insemination elicits inflammatory changes in female reproductive tissues,”^[53]concluding that the changes “likely lead to immunological priming to paternal antigens or influence pregnancy outcomes.” A similar series of studies confirmed the importance of immune modulation in female mice through the absorption of specific immune factors in semen, including TGF-Beta, lack of which is also being investigated as a cause of miscarriage in women andinfertility in men.

According to the theory, pre-eclampsia is frequently caused by a failure of the woman’s immune system to accept the fetus and placenta, which both contain “foreign” proteins from paternal genes. Regular exposure to the father’s semen causes her immune system to develop tolerance to the paternal antigens, a process which is significantly supported by as many as 93 currently identified immune regulating factors in seminal fluid.^[54]^[55] Having already noted the importance of a woman’s immunological tolerance to the fetus’s paternal genes, several Dutch reproductive biologists decided to take their research a step further. Consistent with the fact that human immune systems tolerate things better when they enter the body via the mouth, the Dutch researchers conducted a series of studies that confirmed a surprisingly strong correlation between a diminished incidence of pre-eclampsia and a woman’s practice of oral sex, and noted that the protective effects were strongest if she swallowed her partner’s semen.^[56] The researchers concluded that while any exposure to a partner’s semen during sexual activity appears to decrease a woman’s chances for the various immunological disorders that can occur during pregnancy, immunological tolerance could be most quickly established through oral introduction and gastrointestinal absorption of semen.^[56] Recognizing that some of the studies potentially included the presence of confounding factors, such as the possibility that women who regularly perform oral sex and swallow semen might also engage in more frequent vaginal intercourse, the researchers also noted that, either way, the data still overwhelmingly supports the main theory behind all their studies–that repeated exposure to semen establishes the maternal immunological tolerance necessary for a safe and successful pregnancy.

[edit]Drugs in pregnancy

Main article: Drugs in pregnancy

Drugs used during pregnancy can have temporary or permanent effects on the fetus. Therefore many physicians would prefer not to prescribe for pregnant women, the major concern being over teratogenicity of the drugs. This results in inappropriate treatment of pregnant women. Use of drugs in pregnancy is not always wrong. For example, high fever is harmful for the fetus in the early months. Use of paracetamol is better than no treatment at all. Also, diabetes mellitus during pregnancy may need intensive therapy with insulin. Drugs have been classified into categories A,B,C,D and X based on the Food and Drug Administration(FDA) rating system to provide therapeutic guidance based on potential benefits and fetal risks. Drugs likemultivitamins that have demonstrated no fetal risks after controlled studies in humans are classified as Category A. On the other hand drugs like thalidomide with proven fetal risks that outweigh all benefits are classified as Category X.^[57]

[edit]Sexuality during pregnancy

Most pregnant women can enjoy sexual intercourse throughout gravidity. Most research suggests that, during pregnancy, both sexual desire and frequency of sexual relations decrease.^[58]^[59] In context of this overall decrease in desire, some studies indicate a second-trimester increase, preceding a decrease.^[60] However, these decreases are not universal: a significant number of women report greater sexual satisfaction throughout their pregnancies.^[61]

Sex during pregnancy is a low-risk behaviour except when the physician advises that sexual intercourse be avoided, because it may, in some pregnancies, lead to serious pregnancy complications or health issues such as a high-risk for premature labour or a ruptured uterus. Such a decision may be based upon a history of difficulties in a previous childbirth.

Some psychological research studies in the 1980s and ’90s contend that it is useful for pregnant women to continue to have sexual activity, specifically noting that overall sexual satisfaction was correlated with feeling happy about being pregnant, feeling more attractive in late pregnancy than before pregnancy and experiencing orgasm.^[60] Sexual activity has also been suggested as a way to prepare for induced labour; some believe the natural prostaglandin content of seminal liquid can favour the maturation process of the cervix making it more flexible, allowing for easier and faster dilation and effacement of the cervix. However, the efficacy of using sexual intercourse as an induction agent “remains uncertain”.^[62]

During pregnancy, the fetus is protected from penetrative thrusting by the amniotic fluid in the womb and by the woman’s cervix.^[63]

After giving birth sexual intercourse can begin when the couple are both ready. However most couples wait until after six weeks and they should consult their GP if they have any concerns.^[39]

[edit]Abortion

Main article: Abortion

An abortion is the removal or expulsion of an embryo or fetus from the uterus, resulting in or caused by its death. This can occur spontaneously or accidentally as with a miscarriage, or be artificially induced by medical, surgical or other means.

[edit]Complications and Complaints

[edit]Context

There are fine distinctions between the concepts of fertilization and the actual state of pregnancy, which starts with implantation. In a normal pregnancy, the fertilization of the egg usually will have occurred in the Fallopian tubes or in the uterus. (Often, an egg may become fertilized yet fail to become implanted in the uterus.) If the pregnancy is the result of in-vitro fertilization, the fertilization will have occurred in a Petri dish, after which pregnancy begins when one or more zygotes implant after being transferred by a physician into the woman’s uterus.

In the context of political debates regarding a proper definition of life, the terminology of pregnancy can be confusing. The medically and politically neutral term which remains is simply “pregnancy,” though this can be problematic as it only refers indirectly to the embryo or fetus. De Crespigny observes that doctors’ language has a powerful influence over the way patients think, and thus proposes that the best interests of patients are served by using language that both supports patient autonomy and is neutral.^[68]

[edit]See also

Pregnancy

From Wikipedia, the free encyclopedia

This article is about pregnancy in female humans. For pregnancy in non-human animals, see Gestation. For pregnancy in males, see Male pregnancy.

A pregnant woman near the end of her term

Pregnancy Classification and external resources
ICD-9	V22

[edit]Terminology

The term embryo is used to describe the developing offspring during the first 8 weeks following conception, and the term fetus is used from about 2 months of development until birth.^[7]^[8]

[edit]Progression

Stages in prenatal development, with weeks and months numbered by gestation.

[edit]Initiation

[edit]Perinatal period

Legal regulations in different countries include gestation age beginning from 16 to 22 weeks (5 months) before birth.

[edit]Postnatal period

Main article: Postnatal

[edit]Duration

[edit]Childbirth

Main article: Childbirth

Childbirth is the process whereby an infant is born. It is considered by many to be the beginning of a person’s life, and age is defined relative to this event in most cultures.

During the time immediately after birth, both the mother and the baby are hormonally cued to bond, the mother through the release of oxytocin, a hormone also released duringbreastfeeding.

[edit]Diagnosis

Main article: Obstetrics

[edit]Physiology

The term trimester redirects here. For the term trimester used in academic settings, see Academic term

[edit]First trimester

Comparison of growth of the abdomen between 26 weeks and 40 weeks gestation.

Morning sickness can occur in about seventy percent of all pregnant women and typically improves after the first trimester.^[24]

In the first 12 weeks of pregnancy the nipples and areolas darken due to a temporary increase in hormones. ^[25]

Most miscarriages occur during this period.

A pregnant woman at 26 weeks

[edit]Second trimester

[edit]Third trimester

[edit]Prenatal development and sonograph images

[edit]Physiological changes in pregnancy

The body must change its physiological and homeostatic mechanisms in pregnancy to ensure the fetus is provided for. Increases in blood sugar, breathing and cardiac output are all required.

[edit]Hormonal changes

[edit]Musculoskeletal changes

[edit]Physical changes

[edit]Cardiovascular changes

[edit]Respiratory changes

[edit]Metabolic changes

An increased requirement for nutrients is given by fetal growth and fat deposition. Changes are caused by steroid hormones, lactogen, and cortisol.

Maternal insulin resistance can lead to gestational diabetes. Increase liver metabolism is also seen, with increased gluconeogenesis to increase maternal glucose levels.

[edit]Renal changes

Renal plasma flow increases, as does aldosterone and erthropoietin production as discussed. The tubular maximum for glucose is reduced, which may precipitate gestational diabetes.

[edit]Management

Prenatal medical care is of recognized value throughout the developed world. Periconceptional Folic acid supplementation is the only type of supplementation of proven efficacy.

[edit]Nutrition

Main article: Nutrition and pregnancy

[edit]Weight gain

[edit]Immunological tolerance

Main article: Pre-eclampsia

[edit]Drugs in pregnancy

Main article: Drugs in pregnancy

[edit]Sexuality during pregnancy

During pregnancy, the fetus is protected from penetrative thrusting by the amniotic fluid in the womb and by the woman’s cervix.^[63]

After giving birth sexual intercourse can begin when the couple are both ready. However most couples wait until after six weeks and they should consult their GP if they have any concerns.^[39]

[edit]Abortion

Main article: Abortion

[edit]Complications and Complaints

[edit]Context

[edit]See also

May 27, 2009

Sexual Reproduction in Humans

Posted by sezaz under Sexual Reproduction in Humans
1 Comment

Sexual Reproduction in Humans

Index to this page

The Problems to be Solved

Sexual reproduction is the formation of a new individual following the union of two gametes. In humans and the majority of other eukaryotes — plants as well as animals — the two gametes

differ in structure (“anisogamy”) and
are contributed by different parents.

Gametes need

motility to be able to meet and unite
food to nourish the developing embryo.

In animals (and some plants), these two rather contrasting needs are met by anisogametes:

sperm that are motile (and small)
eggs that contain food.

Sex Organs of the Human Male

The reproductive system of the male has two major functions:

production of sperm
delivery of these to the reproductive tract of the female.

Sperm production — spermatogenesis — takes place in the testes.

Each testis is packed with seminiferous tubules (laid end to end, they would extend more than 20 meters) where spermatogenesis occurs.

Spermatogenesis

The walls of the seminiferous tubules consist of diploid spermatogonia, stem cells that are the precursors of sperm.

Spermatogonia

divide by mitosis to produce more spermatogonia or
differentiate into spermatocytes.

Meiosis of each spermatocyte produces 4 haploid spermatids. This process takes over three weeks to complete.

Then the spermatids differentiate into sperm, losing most of their cytoplasm in the process.

For simplicity, the figure shows the behavior of just a single pair of homologous chromosomes with a single crossover. With 22 pairs of autosomesand an average of two crossovers between each pair, the variety of gene combinations in sperm is very great.

Sperm

Sperm cells are little more than flagellated nuclei. Each consists of

a head, which has
- an acrosome at its tip and
- contains a haploid set of chromosomes in a compact, inactive, state.
a midpiece containing mitochondria and a single centriole
a tail

This electron micrograph (courtesy of Dr. Don W. Fawcett and Susumu Ito) shows the sperm cell of a bat. Note the orderly arrangement of the mitochondria. They supply the ATP to power the whiplike motion of the tail.

An adult male manufactures over 100 million sperm cells each day. These gradually move into the epididymis where they undergo further maturation. The acidic environment in the epididymis keeps the mature sperm inactive.

In addition to making sperm, the testis is an endocrine gland. Its principal hormone, testosterone, is responsible for the development of the secondary sex characteristics of men such as the beard, deep voice, and masculine body shape. Testosterone is also essential for making sperm.

Link to more on testosterone.

Testosterone is made in the interstitial cells that lie between the seminiferous tubules.

LH

Interstitial cells are, in turn, the targets for a hormone often called interstitial cell stimulating hormone (ICSH). It is a product of the anterior lobe of the pituitary gland. However, ICSH is identical to the luteinizing hormone (LH) found in females, and I prefer to call it LH.

FSH

Follicle-stimulating hormone (also named for its role in females) acts directly on spermatogonia to stimulate sperm production (aided by the LH needed for testosterone synthesis). [Discussion]

Sex Organs of the Human Female

The responsibility of the female mammal for successful reproduction is considerably greater than that of the male.

She must

manufacture eggs
be equipped to receive sperm from the male
provide an environment conducive to fertilization and implantation
nourish the developing baby not only before birth but after.

Oogenesis

Egg formation takes place in the ovaries.

In contrast to males, the initial steps in egg production occur prior to birth. Diploid stem cells called oogonia divide by mitosis to produce more oogonia and primary oocytes. By the time the fetus is 20 weeks old, the process reaches its peak and all the oocytes that she will ever possess (~4 million of them) have been formed. By the time she is born, 1–2 million of these remain. Each has

begun the first steps of the first meiotic division (meiosis I) and then
stopped.

No further development occurs until years later when the girl becomes sexually mature. Then the primary oocytes recommence their development, usually one at a time and once a month.

The primary oocyte grows much larger and completes the meiosis I, forming a large secondary oocyte and a small polar body that receives little more than one set of chromosomes. Which chromosomes end up in the egg and which in the polar body is entirely a matter of chance.

In humans (and most vertebrates), the first polar body does not go on to meiosis II, but the secondary oocyte does proceed as far as metaphase ofmeiosis II and then stops.

Only if fertilization occurs will meiosis II ever be completed. Entry of the sperm restarts the cell cycle

breaking down MPF (M-phase promoting factor) and
turning on the anaphase promoting complex (APC).

Completion of meiosis II converts the secondary oocyte into a fertilized egg or zygote (and also a second polar body).

As in the diagram for spermatogenesis, the behavior of the chromosomes is greatly simplified.

The photomicrograph (courtesy of Turtox) shows polar body formation during oogenesis in the whitefish. Even allowing for the fact that fish eggs are larger than mammalian eggs, you can readily see how the polar body gets little more than one set of chromosomes.

These events take place within a follicle, a fluid-filled envelope of cells surrounding the developing egg.

The ripening follicle also serves as an endocrine gland. Its cells make a mixture of steroid hormones collectively known as estrogen. Estrogen is responsible for the development of the secondary sexual characteristics of a mature woman, e.g.,

a broadening of the pelvis
development of the breasts
growth of hair around the genitals and in the armpits
development of adipose tissue leading to the more rounded body contours of adult women.

Estrogen continues to be secreted throughout the reproductive years of women During this period, it plays an essential role in the monthly menstrual cycle.

Link to a discussion of the menstrual cycle and the hormones that regulate it.

There is growing evidence that in mice, at least, oocytes can continue to be produced throughout life (from germline stem cells in the bone marrow). It remains to be seen if that will turn out to be true for humans.

Ovulation

Ovulation occurs about two weeks after the onset of menstruation. In response to a sudden surge of LH, the follicle ruptures and discharges a secondary oocyte. This is swept into the open end of thefallopian tube and begins to move slowly down it.

Several sexually-transmitted diseases (STDs), especially gonorrhea and infections by chlamydia can cause scarring and blocking of the tubes and are a major cause of infertility.
In tubal ligation, the fallopian tubes are surgically cut and their ends tied to prevent pregnancy.

Copulation and Fertilization

For fertilization to occur, sperm must be deposited in the vagina within a few (5) days before or on the day of ovulation. Sperm transfer is accomplished by copulation. Sexual excitation dilates the arterioles supplying blood to the penis. Blood accumulates in three cylindrical spongy sinuses that run lengthwise through the penis. The resulting pressure causes the penis to enlarge and erect and thus able to penetrate the vagina.

Movement of the penis back and forth within the vagina causes sexual tension to increase to the point of ejaculation. Contraction of the walls of each vas deferens propels the sperm along. Fluid is added to the sperm by the seminal vesicles, Cowper’s glands, and the prostate gland. [View] These fluids provide

a source of energy (fructose)
an alkaline environment to activate the sperm, and
perhaps in other ways provide an optimum chemical environment for them.

The mixture of sperm and accessory fluids is called semen. It passes through the urethra and is expelled into the vagina.

Physiological changes occur in the female as well as the male in response to sexual excitement, although these are not as readily apparent. In contrast to the male, however, such responses are not a prerequisite for copulation and fertilization to occur.

Once deposited within the vagina, the sperm proceed on their journey into and through the uterus and on up into the fallopian tubes. It is here that fertilization may occur if an “egg” is present (strictly speaking, it is still a secondary oocyte until after completion of meiosis II).

Although sperm can swim several millimeters each second, their trip to and through the fallopian tubes may be assisted by muscular contraction of the walls of the uterus and the tubes. There is also evidence that they respond to a chemical attractant produced by the egg or the tissues surrounding it [Link]. In any case, sperm may reach the egg within 15 minutes of ejaculation. The trip is also fraught with heavy mortality. An average human ejaculate contains over one hundred million sperm, but only a few dozen complete the journey. And of these, only one will succeed in fertilizing the egg.

Fertilization begins with the binding of a sperm head to the outer coating of the egg (called the zona pellucida). Exocytosis of the acrosome at the tip of the sperm head releases enzymes that digest a path through the zona and enable the sperm head to bind to the plasma membrane of the egg. Fusion of their respective membranes allows the entire contents of the sperm to be drawn into the cytosol of the egg. (Even though the sperm’s mitochondria enter the egg, they are almost always destroyed and do not contribute their genes to the embryo. So human mitochondrial DNA is almost always inherited from mothers only.)

Within moments, enzymes released from the egg cytosol act on the zona making it impermeable to the other sperm that arrive.

Soon the nucleus of the successful sperm enlarges into the male pronucleus. At the same time, the egg (secondary oocyte) completes meiosis II forming a second polar body and the female pronucleus.

The male and female pronuclei move toward each other while duplicating their DNA in S phase. Their nuclear envelopes disintegrate. A spindle is formed (following replication of the sperm’s centriole), and a full set of dyads assembles on it. The fertilized egg or zygote is now ready for its first mitosis. When this is done, 2 cells — each with a diploid set of chromosomes — are formed.

In sea urchins, at least, the block to additional sperm entry and the fusion of the pronuclei are triggered by nitric oxide generated in the egg by the sperm acrosome. [Link]

Pregnancy

Development begins while the fertilized egg is still within the fallopian tube. Repeated mitotic divisions produces a solid ball of cells called a morula. Further mitosis and some migration of cells converts this into a hollow ball of cells called the blastocyst. Approximately one week after fertilization, the blastocyst embeds itself in the thickened wall of the uterus, a process called implantation, and pregnancy is established.

The blastocyst produces two major divisions of cells:

Three or four blastocyst cells develop into the inner cell mass, which will form
- 3 extraembryonic membranes: amnion, yolk sac, and (a vestigial) allantois and
- in about 2 months, become the fetus and, ultimately, the baby.
The remaining 100 or so cells form the trophoblast, which will develop into the chorion that will go on to make up most of the placenta. All the extraembryonic membranes play vital roles during development but will be discarded at the time of birth.

The placenta grows tightly fused to the wall of the uterus. Its blood vessels, supplied by the fetal heart, are literally bathed in the mother’s blood. Although there is normally no mixing of the two blood supplies, the placenta does facilitate the transfer of a variety of materials between the fetus and the mother.

receiving food
receiving oxygen and discharging carbon dioxide
discharging urea and other wastes
receiving antibodies (chiefly of the IgG class). These remain for weeks after birth, protecting the baby from the diseases to which the mother is immune.

But the placenta is not simply a transfer device. Using raw materials from the mother’s blood, it synthesizes large quantities of proteins and also some hormones.

Link to discussion of the placenta
as an endocrine gland.

The metabolic activity of the placenta is almost as great as that of the fetus itself.

The umbilical cord connects the fetus to the placenta. It receives deoxygenated blood from the iliac arteries of the fetus and returns oxygenated blood to the liver and on to the inferior vena cava.

Because its lungs are not functioning, circulation in the fetus differs dramatically from that of the baby after birth. While within the uterus, blood pumped by the right ventricle bypasses the lungs by flowing through the foramen ovale and the ductus arteriosus.

Although the blood in the placenta is in close contact with the mother’s blood in the uterus, intermingling of their blood does not normally occur. However, some of the blood cells of the fetus usually do get into the mother’s circulation — where they have been know to survive for decades. This raises the possibility of doing prenatal diagnosis of genetic disorders by sampling the mother’s blood rather than having to rely on the more invasive procedures of amniocentesis and chorionic villus sampling (CVS).

Far rarer is the leakage of mother’s blood cells into the fetus. However, it does occur. A few pregnant women with leukemia or lymphoma have transferred the malignancy to their fetus. Some babies have also acquired melanoma from the transplacental passage of these highly-malignant cells from their mother.

During the first 2 months of pregnancy, the basic structure of the baby is being formed. This involves cell division, cell migration, and the differentiation of cells into the many types found in the baby. During this period, the developing baby — called an embryo — is very sensitive to anything that interferes with the steps involved. Virus infection of the mother, e.g., by rubella (“German measles”) virus or exposure to certain chemicals may cause malformations in the developing embryo. Such agents are called teratogens (“monster-forming”). The tranquilizer, thalidomide, taken by many pregnant European women between 1954 and 1962, turned out to be a potent teratogen and was responsible for the birth of several thousand deformed babies.

After about two months, all the systems of the baby have been formed, at least in a rudimentary way. From then on, development of the fetus, as it is now called, is primarily a matter of growth and minor structural modifications. The fetus is less susceptible to teratogens than is the embryo.

Pregnancy involves a complex interplay of hormones. These are described in a separate page. [Link to it.]

The placenta is an allograft

One of the greatest unsolved mysteries in immunology is how the placenta survives for 9 months without being rejected by the mother’s immune system. Every cell of the placenta carries the father’s genome (a haploid set of his chromosomes); including one of his #6 chromosomes where the genes for the major histocompatibility antigens are located.

One partial exception: none of the genes on the father’s X chromosome are expressed. While X-chromosome inactivation is random in the cells of the fetus, it is NOT random in the cells of the trophoblast. In every cell of the trophoblast — and its descendants — it is the paternal X chromosome that is inactivated. [Discussion of X-chromosome inactivation.] But this does not solve our problem because the genes for all the major histocompatibility antigens are located on chromosome 6, which is not inactivated.

Discussion of the human major histocompatibility complex (MHC)

Thus the placenta is immunologically as foreign to the mother as a kidney transplant would be.

Yet it thrives.

Despite a half-century of research, the mechanism for this immunologically privileged status remains uncertain. But one thing is clear:

The mother is not intrinsically tolerant of the father’s antigens.

Some evidence:

She will promptly reject a skin transplant from the father.
She develops antibodies against his histocompatibility antigens expressed by the fetus. In fact, women who have borne several children by the same father are often excellent sources of anti-HLA serum for use in tissue typing.

So what accounts for the phenomenon? Some possibilities:

The placenta does not express class II histocompatibility antigens.

Discussion of the role of class II antigens in immunity.
Nor does it express the strongly-immunogenic class I histocompatibility antigens (HLA-A, HLA-B). It does express HLA-C, but this is only weakly immunogenic.
The cells of the placenta secrete progesterone, which is immunosuppressive.

In lab rats the embryos (and the mother’s endometrium) secrete corticotropin-releasing hormone (CRH). This hormone induces the expression of Fas ligand (FasL) on the cells of the placenta. Activated T cells express Fas so any threatening T cells would commit suicide by apoptosis when they encounter FasL on their target.

Link to more of the story of the role of Fas and FasL in apoptosis. (but note: the example you will see is the reverse of the story here; that is, the cytotoxic T cell is using its own FasL to kill a target cell that is expressing Fas but not FasL.)

In laboratory mice the cells of the placenta degrade the amino acid tryptophan. Tryptophan is essential for T-cell function. When mice are treated with an inhibitor of the Trp-degrading enzyme, their fetuses are promptly aborted by the action of the mother’s lymphocytes. (D. H. Munn, et. al., Science, 281: 1191, 21 Aug 1998.)
Perhaps most important of all is the increased production in the mother of immunosuppressive regulatory T cells (Treg).
- Depletion of Treg cells in pregnant mice leads to spontaneous abortion while
- injection of Treg cells into mice that are otherwise prone to abortion enables them to carry their fetuses to term.
- In humans, the number of Treg cells rises sharply during pregnancy.

Assisted Reproductive Technology (“ART”)

On July 25, 2008 Louise Brown celebrated her 30th birthday. She was the first of what today number some four million (worldwide) “test tube babies”; that is, she developed from an egg that was fertilized outside her mother’s body — the process called in vitro fertilization (IVF).

In Vitro Fertilization (IVF)

IVF involves

harvesting mature eggs from the mother. This is not an easy process. The mother must undergo hormonal treatments to produce multiple eggs, which then must be removed (under anesthesia) from her ovaries.
harvesting sperm from the father. Harvesting is usually no problem, but often the sperm are defective in their ability to fertilize (so setting the stage for ICSI);
mixing sperm and eggs in a culture vessel (“in vitro”);
culturing the fertilized eggs for several days until they have developed to at least the 8-cell stage;
placing two or more of these into the mother’s uterus (which her hormone treatments have prepared for implantation);
keeping one’s fingers crossed — only about one-third of the attempts result in a successful pregnancy)

Intracytoplasmic Sperm Injection (ICSI)

Successful IVF assumes the availability of healthy sperm. But many cases of infertility arise from defects in the father’s sperm. Often these can be overcome by directly injecting a single sperm into the egg.

In the U.S. today, some two-thirds of ART procedures employ ICSI (even though most of these do not involve male infertility).

Ooplasmic Transfer

Infertility in some cases may stem from defects in the cytoplasm of the mother’s egg. To circumvent these, cytoplasm can be removed from the egg of a young, healthy woman (“Donor egg”) and injected — along with a single sperm — into the prospective mother’s egg.

Several dozen children have been born by this method, but it is not yet approved for general use in the U.S.

One reason for concern is that ooplasmic transfer results in an egg carrying both the mother’s mitochondria and mitochondria from the donor. This condition — calledheteroplasmy — creates a child having two different mitochondrial DNA genomes in all of its cells.

In normal fertilization, all the mitochondria in the father’s sperm are destroyed in the egg, and perhaps this is important. Although a few healthy children have been born following ooplasmic transfer, the jury is still out on its safety.

The Upside of ART

It has allowed some four million previously-infertile couples to have children.
It permits screening (on one cell removed from the 8-celled morula) for the presence of genetic disorders — thus avoiding starting a pregnancy if a disorder is found.

Link to a discussion.
One can use frozen sperm allowing fatherhood for a man who is no longer able to provide fresh sperm.
Because a number of morulas are created, the extras can be frozen, stored, and used later
- if the initial attempt fails (the prospective mother must still receive hormones to prepare her uterus for implantation and the success rate is lower with thawed morulas).
- Where regulations permit, the extras can be used as a source of embryonic stem (ES) cells.
  
  Discussion

The Downside of ART

Although improving, the success rate is still sufficiently low (~35%) that the process often has to be repeated.
Because several morulas are usually transferred, multiple births are common (about 50%), and as is the case with most multiple births, the babies are born early and weigh less. To reduce the number of twins, triplets, etc., more ART centers are turning to “single-embryo transfer” (SET). Some ART centers find that they can increase the success rate — and thus rely more on SET — by culturing the morulas for 5–6 days, instead of the usual 2–3 days, before transferring them (by now they have become blastocysts) to the mother.
The risk of birth defects is about doubled (from ~4% in “normal” pregnancies to ~8% in ART pregnancies).
ART procedures in experimental animals often result in a failure of correct gene imprinting. Whether this will pose a problem for humans remains to be seen.

Birth and Lactation

Exactly what brings about the onset of labor is still not completely understood. Probably a variety of integrated hormonal controls are at work.

Link to a discussion of hormones involved in birth and lactation.

The first result of labor is the opening of the cervix. With continued powerful contractions, the amnion ruptures and the amniotic fluid (the “waters”) flows out through the vagina. The baby follows, and its umbilical cord can be cut.

The infant’s lungs expand, and it begins breathing. This requires a major switchover in the circulatory system. Blood flow through the umbilical cord, ductus arteriosus, and foramen ovale ceases, and the adult pattern of blood flow through the heart, aorta, and pulmonary arteries begins. In some infants, the switchover is incomplete, and blood flow through the pulmonary arteries is inadequate. Failure to synthesize enough nitric oxide (NO) is one cause.

Shortly after the baby, the placenta and the remains of the umbilical cord (the “afterbirth”) are expelled.

At the time of birth, and for a few days after, the mother’s breasts contain a fluid called colostrum. It is rich in calories and protein, including antibodies that provide passive immunity for the newborn infant.

Three or four days after delivery, the breasts begin to secrete milk.

Its synthesis is stimulated by the pituitary hormone prolactin (PRL).
Its release is stimulated by a rise in the level of oxytocin when the baby begins nursing.
Milk contains an inhibitory peptide. If the breasts are not fully emptied, the peptide accumulates and inhibits milk production. This autocrine action thus matches supply with demand.

Birth Control

Methods of birth control are discussed on a separate page. Link to it.

Welcome&Next Search

22 February 2009

Embryo at 4 weeks after fertilization^[31]	Fetus at 8 weeks after fertilization^[32]	Fetus at 18 weeks after fertilization^[33]	Fetus at 38 weeks after fertilization^[34]
Relative size in 1st month (simplified illustration)	Relative size in 3rd month (simplified illustration)	Relative size in 5th month (simplified illustration)	Relative size in 9th month (simplified illustration)

Embryo at 4 weeks after fertilization^[31]	Fetus at 8 weeks after fertilization^[32]	Fetus at 18 weeks after fertilization^[33]	Fetus at 38 weeks after fertilization^[34]
Relative size in 1st month (simplified illustration)	Relative size in 3rd month (simplified illustration)	Relative size in 5th month (simplified illustration)	Relative size in 9th month (simplified illustration)

Pregnancy

Methods

[edit]Physical methods

[edit]Barrier methods

[edit]Hormonal methods

[edit]Ormeloxifene (Centchroman)

[edit]Emergency contraception

[edit]Intrauterine methods

[edit]Sterilization

[edit]Behavioral methods

[edit]Fertility awareness

[edit]Coitus interruptus

[edit]Avoiding vaginal intercourse

[edit]Lactational

[edit]Induced abortion

[edit]Methods in development

[edit]For females

[edit]For males

[edit]Misconceptions

[edit]Effectiveness

[edit]Protection against sexually transmitted infections

[edit]Religious and cultural attitudes

[edit]Religious views on birth control

[edit]Birth control education

From Wikipedia, the free encyclopedia

Contents

[edit]History

Pregnancy

From Wikipedia, the free encyclopedia

Contents

[edit]Terminology

[edit]Progression

[edit]Initiation

[edit]Perinatal period

[edit]Postnatal period

[edit]Duration

[edit]Childbirth

[edit]Diagnosis

[edit]Physiology

[edit]First trimester

[edit]Second trimester

[edit]Third trimester

[edit]Prenatal development and sonograph images

[edit]Physiological changes in pregnancy

[edit]Hormonal changes

[edit]Musculoskeletal changes

[edit]Physical changes

[edit]Cardiovascular changes

[edit]Respiratory changes

[edit]Metabolic changes

[edit]Renal changes

[edit]Management

[edit]Nutrition

[edit]Weight gain

[edit]Immunological tolerance

[edit]Drugs in pregnancy

[edit]Sexuality during pregnancy

[edit]Abortion

[edit]Complications and Complaints

[edit]Context

[edit]See also

Pregnancy

From Wikipedia, the free encyclopedia

Contents

[edit]Terminology

[edit]Progression

[edit]Initiation

[edit]Perinatal period

[edit]Postnatal period

[edit]Duration

[edit]Childbirth

[edit]Diagnosis

[edit]Physiology

[edit]First trimester

[edit]Second trimester

[edit]Third trimester

[edit]Prenatal development and sonograph images

[edit]Physiological changes in pregnancy

[edit]Hormonal changes

[edit]Musculoskeletal changes