The earliest a doctor can make the diagnosis of pregnancy is when the period is two or three weeks late: in other words, six to seven weeks front the previous menstruation period. By this time the uterus is appreciably enlarged and softened. Because of the increased blood supply to the uterus, its neck, the cervix, takes on a bluish coloration that is suggestive of early pregnancy. Tests done on a sample of urine or blood are helpful in establishing the diagnosis of pregnancy. There is a good chance of getting a positive pregnancy test by the time the p&iod is ten days late, and within another two or three weeks almost all women with normal pregnancies show positive results.
Usually a test is done only when there is much urgency, either medical or social. for establishing the diagnosis of
pregnancy; in a few days more the results of an internal examination will be conclusive. All pregnancy tests detect the presence of the hormone chorionic gonadotropin in the blood and urine. This hormone now is being elaborated by the placenta. which is one of the most important structures developed in pregnancy. (Its common name is the afterbirth.) The placenta is involved in both the nourishment of the fetus and the elimination of the fetal waste products
. We shall have more to say about this organ later. The oldest of the biologic tests for pregnancy is still one of the most dependable. This is the Ascheim-Zondek or AZ lest. Immature white rats are injected with a sample of blood serum or urine, and if chorionic gonadotropin is present. enlargement and redness of the ovaries are noted when the animals are sacrificed twenty-four hours later. The AZ test has the advantage of being very sensitive but the disadvantage of taking the longest to perform. In common with other biologic tests for pregnancy, the errors that arise are “false negatives.” In these cases, the woman is actually pregnant but the result of the test is negative. “False positives” hardly ever occur.
If the result comes back positive, it is most unlikely that the woman is not pregnant. Pregnancy tests of all kinds generally cost the patient from $5 to $10, depending on the local laboratory charge. A more rapid pregnancy test uses a male frog. If chorionic gonadotropin is present, it will induce the appearance of sperm cells in the cloacal fluid. Since frogs are much easier to handle than white rats, the frog test is more convenient for the laboratory to perform and much quicker, taking only four to five hours. The newest and fastest test is based upon an immunologic reaction involving the woman’s urine, a serum taken from rabbits, and pure human chorionic gonadotropin. These immunologic tests can be done in minutes or a couple of hours at most and save the laboratory from having to maintain colonies of animals.
While false positives have been somewhat more common than with other types of tests, the sensitivity. convenience. and rapidity make up for the errors. Most pregnancy tests done today are of this general type. When the menstrual period is a few days late, some women not anxious to conceive ask the doctor for a pill or shot to “bring on the period ” The administration of progesterone will induce vaginal bleeding in two or three days in nonpregnant women. This bleeding is similar to a menstrual period, but may not be of the usual amount or duration.