19-01: Diagnosis of Pregnancy

It is advantageous to diagnose pregnancy as promptly as possible. Prenatal care can begin early for a desired pregnancy, and potentially harmful medications and activities such as drug and alcohol use, smoking, and occupational chemical exposure can be eliminated. If an unwanted pregnancy occurs, counseling about options can be provided at an early stage.

PREGNANCY TESTS

All urine or blood pregnancy tests rely on the detection of human chorionic gonadotropin (hCG) produced by the placenta. Levels increase shortly after implantation, approximately double every 48 hours (this rise can range from 30% to 100% in normal pregnancies), reach a peak at 50–75 days, and fall to lower levels in the second and third trimesters. Pregnancy tests are performed on serum or urine and are accurate at the time of the missed period or shortly after it.

Compared with intrauterine pregnancies, ectopic pregnancies may show lower levels of hCG that plateau or fall in serial determinations. Quantitative assays of hCG repeated at 48-hour intervals are used in the diagnosis of ectopic pregnancy as well as in cases of molar pregnancy and early pregnancy loss. Comparison of hCG levels between laboratories may be misleading in a given patient because different international standards may produce results that vary by as much as twofold. Consistent follow-up is necessary to make the correct diagnosis and management plan. Pregnancy of unknown location is a term used to describe a situation where a woman has a positive pregnancy test, but the location and viability of the pregnancy are not known because it is not seen on transvaginal ultrasound.

MANIFESTATIONS OF PREGNANCY

The following symptoms and signs are usually due to pregnancy, but none are diagnostic. A record of the time of coitus or insemination is helpful for diagnosing and dating a pregnancy.

A. Symptoms

Amenorrhea, nausea and vomiting, breast tenderness and tingling, urinary frequency and urgency, “quickening” (perception of first movement noted at about the 18th week), weight gain.

B. Signs (in Weeks From Last Menstrual Period)

Breast changes (enlargement, vascular engorgement, colostrum) begin early in pregnancy and continue until the postpartum period. Cyanosis of the vagina and cervical portio and softening of the cervix occur in about the 7th week. Softening of the cervicouterine junction takes place in the 8th week, and generalized enlargement and diffuse softening of the corpus occurs after the 8th week. When a woman’s abdomen will start to enlarge depends on her body habitus but typically starts in the 16th week.

The uterine fundus is palpable above the pubic symphysis by 12–15 weeks from the last menstrual period and reaches the umbilicus by 20–22 ...