pregnancy, period of time between fertilization of the ovum (conception) and birth, during which mammals carry their developing young in the uterus (see embryo). The duration of pregnancy in humans is about 280 days, equal to 9 calendar months. After the fertilized ovum is implanted in the uterus, rapid changes occur in the reproductive organs of the mother. The uterus becomes larger and more flexible, enlargement of the breasts begins, and alteration of renal function, blood volume, and blood cell count occur. Movement of the fetus and fetal heartbeat can be detected early in pregnancy.

One test that has been used to determine pregnancy uses blood or urine samples to detect a hormone known as BhCG, found exclusively in pregnant women. Later, prenatal diagnostic tests such as alpha fetoprotein, amniocentesis, and chorionic villus sampling may be performed as screening measures for congenital defects. Ultrasound, a sonar device using high-frequency wavelengths, is used to detect defects, measure fetal heartbeat, and monitor growth of a fetus.

Complications of pregnancy include eclampsia, premature birth, and erythroblastosis fetalis (Rh incompatibility). Ectopic pregnancy, in which the fetus begins to develop outside the uterus, often in a fallopian tube, is another complication. It is often the result of scarring from a sexually transmitted disease. Smoking has been linked to low-birth weight infants; alcohol consumption during pregnancy has been linked to a group of defects called fetal alcohol syndrome.

The technology relating to pregnancy has made great advances and has created a number of ethical issues. Many women in their 40s are now able to sustain successful pregnancies, due to technological devices that carefully monitor the progress of the fetus. In vitro fertilization and other infertility treatments have allowed even postmenopausal women to give birth. The use of fertility drugs has led to a marked increase in multiple births. Abortion, in which pregnancy is terminated prior to birth, has long been a subject of heated debate, and surrogate motherhood (see surrogate mother) has also raised ethical issues in recent years.

See also amenorrhea; birth defects; midwifery.

Expulsion of a fetus from the uterus before it can survive on its own. Spontaneous abortion at earlier stages of pregnancy is called miscarriage. Induced abortions often occur through intentional medical intervention and are performed to preserve the woman’s life or health, to prevent the completion of a pregnancy resulting from rape or incest, to prevent the birth of a child with serious medical problems, or because the woman does not believe she is in a position to rear a child properly. The drug RU-486, if taken within a few weeks of conception, will trigger a miscarriage. Up to about 19 weeks of pregnancy, injections of saline solutions or hormones may be used to stimulate uterine contractions that will expel the fetus. Surgical removal of the contents of the uterus may be performed in the second trimester or later. Intact dilation and extraction procedures may occur in the third trimester; sometimes critically referred to as “partial-birth abortions,” they have been very controversial. Other abortion procedures include manual vacuum aspiration (extraction by manual syringe) and dilation and suction curettage (extraction by machine-operated suction), both of which can be performed in early pregnancy. The social acceptability of abortion as a means of population control has varied from time to time and place to place throughout history. It was apparently a common method of family limitation in the Greco-Roman world, but Christian theologians early and vehemently condemned it. It became widely accepted in Europe in the Middle Ages. Severe criminal sanctions to deter abortion became common in the 19th century, but in the 20th century those sanctions were gradually modified in many countries. In the U.S. the 1973 Roe v. Wade decision had the effect of legalizing abortion during the first three months of pregnancy; states were able to implement restrictions on access to abortion after the first trimester, though within constraints set by the courts. Since that decision, there has been a fierce debate between supporters and opponents of a liberalized abortion policy.

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Process of human gestation that takes place in the female's body as a fetus develops, from fertilization to birth (see parturition). It begins when a viable sperm from the male and egg from the ovary merge in the fallopian tube (see fertility; fertilization). The fertilized egg (zygote) grows by cell division as it moves toward the uterus, where it implants in the lining and grows into an embryo and then a fetus. A placenta and umbilical cord develop for nutrient and waste exchange between the circulations of mother and fetus. A protective fluid-filled amniotic sac encloses and cushions the fetus. Early in pregnancy, higher estrogen and progesterone levels halt menstruation, cause nausea, often with vomiting (morning sickness), and enlarge the breasts and prepare them for lactation. As the fetus grows, so does the uterus, displacing other organs. Normal weight gain in pregnancy is 20–25 lbs (9–11.5 kg). The fetus's nutritional needs require the mother to take in more calories and especially protein, water, calcium, and iron. Folic-acid supplements are recommended during early pregnancy to prevent neural tube defects. Smoking, alcohol, and many legal and illegal drugs can cause congenital disorders and should be avoided during pregnancy. Ultrasound imaging is often used to monitor structural and functional progress of the growing fetus. The due date is estimated as 280 days from the time of last menstruation; 90percnt of babies are born within two weeks of the estimated date. Seealso amniocentesis; preeclampsia and eclampsia; premature birth.

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or extrauterine pregnancy

Condition in which a fertilized egg is imbedded outside the uterus (see fertilization). Early on, it may resemble a normal pregnancy, with hormonal changes, amenorrhea, and development of a placenta. Later, most patients have pain as the growing embryo stretches the structure it is attached to. Rupture may cause life-threatening bleeding. A tubal pregnancy may result from obstruction of the egg's passage through the fallopian tube. In an ovarian pregnancy, the egg is fertilized before it leaves the ovary. Implantation elsewhere in the abdomen is an abdominal pregnancy.

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