Other conditions may confuse the diagnosis of pregnancy. Absence of menstruation can be caused by chronic illness, by emotional or endocrine disturbances, by fear of pregnancy, or by a desire to be pregnant. Nausea and vomiting may be of gastrointestinal or psychic origin. Tenderness of the breasts can be due to a hormonal disturbance.
Any condition that causes pelvic congestion, such as a pelvic tumour, may cause duskiness of the genital tissues. At times a soft tumour of the uterus may simulate a pregnancy. The question of pregnancy may be raised if the woman does not menstruate regularly; the absence of other symptoms and signs of gestation indicates that she is not pregnant. There are rare ovarian and uterine tumours that produce false-positive pregnancy tests. It may be difficult for the physician to exclude pregnancy on the basis of an examination if the uterus is tipped back and difficult to feel, or if it is enlarged by a tumour within it. If other signs of pregnancy are absent, however, and the tests for pregnancy are negative, pregnancy can most likely be ruled out.
Childless women who greatly desire a baby sometimes suffer from false or spurious pregnancy (pseudocyesis). They stop menstruating, have morning nausea, “feel life,” and have abdominal enlargement caused by fat and intestinal gas. At “term” they may have “labour pains.” Signs of pregnancy are absent. Treatment is by psychotherapy.
Menopausal women often fear pregnancy when their periods stop; information that they show no signs of pregnancy usually reassures them. Retained uterine secretions of bloody or watery fluid, caught above a blocked mouth of the uterus (cervix), prevent menstruation, cause softening and enlargement of the uterus, and may cause the patient to wonder whether she is pregnant. There are no other signs of pregnancy, and the hard cervix, closed by scar tissue, explains the problem.
Duration of pregnancy
There are, as a rule, 266 to 270 days between ovulation and childbirth, with extremes of 250 and 285 days. Physicians usually determine the date of the estimated time for delivery by adding seven days to the first day of the last menstrual period and counting forward nine calendar months; i.e., if the last period began on January 10, the date of delivery is October 17. Courts of law, in determining the legitimacy of a child, may accept much shorter or much longer periods of gestation as being within the periods of possible duration of a pregnancy. One court in the state of New York has accepted a pregnancy of 355 days as legitimate. British courts have recognized 331 and 346 days as legitimate with the approval of medical consultants. Fully developed infants have been born as early as 221 days after the first day of the mother's last menstrual period.
Because the exact date of ovulation is usually not known, it is seldom possible to make an accurate estimate of the date of delivery. There is a 5 percent chance that a baby will be born on the exact date estimated from the above rule. There is a 25 percent chance that it will be born within four days before or after the estimated date. There is a 50 percent chance that delivery will occur on the estimated date plus or minus seven days. There is a 95 percent chance that the baby will be born within plus or minus 14 days of the estimated date of delivery. (John W. Huffman)
Additional Reading
General texts include Human Embryology, 4th ed. by W.J. Hamilton and H.W. Mossman (1972); and Williams Obstetrics, 19th ed. by F. Gary Cunningham et al. (1993), a standard textbook in the field. Additional information may be found in the following specialized texts: Irwin R. Merkatz and Joyce E. Thompson (eds.), New Perspectives on Prenatal Care (1990); Robert K. Creasy and Robert Resnik (eds.), Maternal-Fetal Medicine: Principles and Practice, 3rd ed. (1994); Burwell and Metcalfe's Heart Disease and Pregnancy, 2nd ed. by James Metcalfe, John H. McAnulty, and Kent Ueland (1986); and Richard S. Abrams, Handbook of Medical Problems During Pregnancy(1989).
John W. Huffman Ed.
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