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 average 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.

See J. T. Queenan and C. N. Queenan, ed. A New Life (1992); C. A. Bean, Methods of Childbirth (1990);; Boston Women's Health Book Collective, Our Bodies, Ourselves for the New Century (1998).

The Columbia Encyclopedia, 6th ed. Copyright© 2014, The Columbia University Press.

Selected full-text books and articles on this topic

Pregnancy, Birth, and the Early Months: The Thinking Woman's Guide
Richard I. Feinbloom.
Perseus Publishing, 2000 (3rd edition)
Risk, Age and Pregnancy: A Case Study of Prenatal Genetic Screening and Testing
Bob Heyman; Mette Henriksen.
Palgrave, 2001
Pregnancy for Older Women: Assessing the Medical Risks
Phyllis Kernoff Mansfield.
Praeger, 1986
Postponing Parenthood: The Effect of Age on Reproductive Potential
Gale A. Sloan.
Insight Books, 1993
Prenatal Testing: A Sociological Perspective
Aliza Kolker; B. Meredith Burke.
Bergin & Garvey, 1994
Mother and Fetus: Changing Notions of Maternal Responsibility
Robert H. Blank.
Greenwood Press, 1992
Understanding Genetics: A Primer for Couples and Families
Angela Scheuerle.
Praeger, 2005
Librarian’s tip: Part II "Pregnancy and Pregnancy Planning"
Fetal Protection in the Workplace: Women's Rights, Business Interests, and the Unborn
Robert H. Blank.
Columbia University Press, 1993
A Time to Be Born: Customs and Folklore of Jewish Birth
Michele Klein.
Jewish Publication Society, 1998
Birth Alternatives: How Women Select Childbirth Care
Sandra Howell-White.
Greenwood Press, 1999
Birth by Design: Pregnancy, Maternity Care, and Midwifery in North America and Europe
Raymond Devries; Sirpa Wrede; Edwin Van Teijlingen; Cecilia Benoit.
Routledge, 2001
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