Tests for Pregnancy Diagnosis

At the present time there are four criteria for the presence of pregnancy. The first criterion is a positive reaction to a biological test for pregnancy.
Pregnancy Tests

Hormonal products of conception, present in the urine of pregnant women, have a remarkably stimulating effect on the ovaries of young mice. This is the basis of the Ascheim-Zondek or AZ Test for pregnancy, first described over 30 years ago. The test is first definitely positive about four weeks after fertilization takes place, or six weeks after the last menstrual period.

The test requires a specimen of the patient’s urine, taken first thing in the morning on awakening. Preferably the patient does not eat or drink after eight or nine p.m. the night before. The evening meal should be bland, without alcohol, drugs or seasoned foods which will leave products in the urine that can kill the test animals. Small amounts of urine are injected into mice over a three-day period. Pregnancy is indicated by obvious activity in ovaries of the mice. The test is most reliable, on the order of 95 to 98 per cent.

“Faster” tests have largely superseded the original AZ Test. The “rat test” and “rabbit test,” almost as reliable as the original mouse test, take about 24 hours instead of three days. In the past decade the “frog test,” performed in three to five hours, has become popular. These animal tests are usually performed with a urine specimen but they may be performed with blood. The latter can be done more promptly since it is not necessary to wait until early morning for a urine specimen. The frog test is usually more dependable when pregnancy is a little further advanced. It is advisable to wait until about seven weeks after the last menstrual period for the frog test, whereas the other animal tests are usually reliable about a week earlier.

A number of so-called agglutination tests which do not require the use of animals have recently been devised. These depend on reaction of an antibody against the hormone excreted by the developing placenta. If small clumped particles appear when the urine and the antibody are warmed together in a tube, pregnancy is indicated. These tests are easily performed but not quite so reliable as the animal tests.

A number of hormone preparations useful in diagnosing pregnancy are available. These are called progestins and are closely related to the natural hormone, progesterone, which is produced during every normal menstrual cycle. If one of these progestins is injected or given by mouth for four or five days, the patient, if not pregnant, will bleed two to seven days after the last dose. If she is pregnant there is no bleeding (called with­drawal bleeding), because her body and the early developing fetus are producing large amounts of progesterone, and the small amount given for the test does not significantly change the body level. In a non-pregnant woman, withdrawal of the progestin produces uterine bleeding just as occurs in a normal menstrual cycle. These compounds are not of the same degree of reliability as the biological tests for pregnancy.

Animal tests are very accurate, though an occasional doubtful result requires repetition. Usually, two or three animals are injected with the same urine specimen, and if all are “positive,” pregnancy is virtually certain. It is important to use a laboratory that performs these tests every day, since accuracy is reduced if technicians do the tests infrequently.

The second positive test for pregnancy is the presence of the fetal skeleton, shown by direct x-ray film of the abdomen. It takes about four months of pregnancy for sufficient calcification to occur to make the fetal skeleton visible on an x-ray film.

The third reliable indicator of pregnancy is fetal movements. The patient may “feel life” between the sixteenth and twentieth weeks. She may misinterpret intestinal and muscular activity as movements of the fetus, but the trained physician may easily discern definitive movements of the infant by palpating the abdomen of the patient.

The fourth indicator of pregnancy is the infant’s heartbeat, distinguishable at the eighteenth week (infrequently, the sixteenth week). With a stethoscope, the rapid fetal heart rate is easily distinguished from that of the mother.