Pregnancy tests are based on the presence of human chorionic gonadotropin (hCG). This hormone, made by the blastocyst as early as the fourth day of its existence, and later by the developing placenta, is sent into the motherís bloodstream and excreted in her urine. It can thus be detected in either blood or urine. Todayís methods can detect hCG in minute amounts.
The most commonly used pregnancy tests today for both in-office and at-home pregnancy testing actually test for an antibody that is specific to a particular part of hCG, called the beta subunit. These tests are approximately 99 percent accurate and can detect pregnancy as early as the first day of the missed menstrual period. The test directions must be followed very carefully and if a test is negative, it should be repeated in a week if menses hasnít yet occurred.
A physical examination of a pregnant woman reveals that virtually every organ and tissue of the body is affected to some degree by the physiologic change of pregnancy. These changes result, directly or indirectly, from the action of the chemicals produced by the placenta - the afterbirth. The placentaís primary function is to deliver oxygen and good essentials from the motherís bloodstream to the baby and to excrete the babyís waste products. [an error occurred while processing this directive]