Diagnosis
Many women first discover they are pregnant after a positive home pregnancy test. Pregnancy urine tests check for the presence of human chorionic gonadotropin (hCG), which is produced by a placenta. Home tests can detect pregnancy on the day of the missed menstrual period.
Home pregnancy tests are more than 97% accurate if the result is positive, and about 80% accurate if the result is negative. If the result is negative and there is no menstrual period within another week, the pregnancy test should be repeated. While home pregnancy tests are very accurate, they are less accurate than a pregnancy test evaluated by a laboratory. For this reason, a woman may want to consider having a second pregnancy test conducted at her doctor's office to be sure of the accuracy of the result.
Blood tests to determine pregnancy are usually used only when a very early diagnosis of pregnancy is needed. This more expensive test, which also looks for hCG, can produce a result within 9–12 days after conception.
Once pregnancy has been confirmed, there are a range of screening tests that can be done to screen for birth defects, which affect about 3% of unborn children. Two tests are recommended for all pregnant women: alpha-fetoprotein (AFP) and the triple marker test.
Other tests are recommended for women at higher risk for having a child with a birth defect. These groups include women over age 35 who had another child or a close relative with a birth defect, or who have been exposed to certain drugs or high levels of radiation. Women with any of these risk factors may want to consider amniocentesis, chorionic villus sampling (CVS) or ultrasound.
Other Prenatal Tests
There are a range of other prenatal tests that are routinely performed, including:
- * pap test
- * gestational diabetes screening test at 24–28 weeks
- * tests for sexually transmitted diseases
- * urinalysis
- * blood tests for anemia or blood type
- * screening for immunity to various diseases, such as German measles