Pregnancy Test Before Missed Period Accuracy
Symptoms and Signs; Biological Tests of Pregnancy
Outward early indications of pregnancy are missed menstrual periods, morning nausea, and fullness and tenderness of the breasts; but the positive and certain signs of gestation are the sounds of the fetal heartbeat, which are audible with a stethoscope between the 16th and the 20th week of pregnancy; ultrasound images of the growing fetus, which can be observed throughout pregnancy; and fetal movements, which usually occur by the 18th to the 20th week of pregnancy.
Persons who note their body temperature upon awakening, as many women do who wish to know when they are ovulating, may observe continued elevation of the temperature curve well beyond the time of the missed period; this is strongly suggestive of pregnancy.
During the early months of pregnancy, women may notice that they urinate frequently, because of pressure of the enlarging uterus on the bladder; feel tired and drowsy; dislike foods that were previously palatable; have a sense of pelvic heaviness; and are subject to vomiting (which can be severe) and to pulling pains in the sides of the abdomen, as the growing uterus stretches the round ligaments that help support it, singly or together. Most of these symptoms subside as pregnancy progresses. The signs and symptoms of pregnancy are so definite by the 12th week that the diagnosis is seldom a problem.
Biological tests for pregnancy depend upon the production by the placenta (the temporary organ that develops in the womb for the nourishing of the embryo and the elimination of its wastes) of chorionic gonadotropin, an ovary-stimulating hormone.
In practice, the tests have an accuracy of about 95 percent, although false-negative tests may run as high as 20 percent in a series of cases. False-negative reports are frequently obtained during late pregnancy when the secretion of chorionic gonadotropin normally decreases. The possibility not only of false-negative but also of false-positive tests makes the tests, at best, probable rather than absolute evidence of the presence or absence of pregnancy. Chorionic gonadotropin in a woman’s blood or urine indicates only that she is harbouring living placental tissue. It does not tell anything about the condition of the fetus. In fact, the greatest production of chorionic gonadotropin occurs in certain placental abnormalities and disorders that can develop in the absence of a fetus.
Tests using immature mice (the Aschheim-Zondek test) and immature rats have been found to be extremely accurate. Tests using rabbits (the Friedman test) have been largely replaced by the more rapid and less expensive frog and toad tests.
The use of the female South African claw-toed tree toad, Xenopus laevis, is based on the discovery that this animal will ovulate and extrude visible eggs within a few hours after it has received an injection of a few millilitres of urine from a pregnant woman. The male common frog, Rana pipiens, will extrude spermatozoa when treated in the same way. Both of these tests are considered somewhat unsatisfactory because false-positive reactions are not uncommon.
Several immunological reaction tests in common use are based upon the inhibition of hemagglutination (clotting of red cells). A positive test is obtained when human chorionic gonadotropin (HCG) in the woman’s urine or blood is added to human chorionic gonadotropin antiserum (rabbit blood serum containing antibodies to HCG) in the presence of particles (or red blood cells) coated with human chorionic gonadotropin. The hormone from the woman will inhibit the combination of coated particles and antibody, and agglutination does not occur. If there is no chorionic gonadotropin in her urine, agglutination will occur and the test is negative.
Several “signs” noted by the physician during an examination will suggest that a patient may be in the early months of pregnancy. Darkening of the areola of the breast (the small, coloured ring around the nipple) and prominence of the sebaceous glands around the nipple (Montgomery’s glands); purplish-red discoloration of the vulvar, vaginal, and cervical tissues; softening of the cervix and of the lower part of the uterus and, of course, enlargement and softening of the uterus itself are suggestive but not necessarily proof of pregnancy.
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About the Author
Nelson Ndalila is an infertility expert from Nottingham. He can be reached through his blog infertilityhospital.blogspot.com
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