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The three prenatal tests that are also known as genetic tests in common use are amniocentesis, chorionic villi sampling (CVS), and alpha-fetoprotein (AFP).
Amniocentesis and CVS are used to determine whether or not your baby has any one of about 200 to 300 metabolic and chromosomal disorders out of 3,000 known genetic defects. Ordinarily, however, your fetal sample will not be tested for all possible disorders. AFP and the triple marker test are used primarily to screen for neural tube defects.
At least three-fourths of amniocentesis and CVS tests are given to women because they are age 35 or older, theoretically because the risk of miscarriage from the procedure is less than the risk for Down Syndrome. These tests may also be performed when a woman has a previous child with a birth defect or when there is a family history of birth defects, including Down's Syndrome, Duchenne muscular dystrophy, hemophilia, cystic fibrosis, or neural tube defects, among others.
Prenatal testing is also often recommended if the pregnant woman has a history of miscarriage, if her mate's previous wife had a history of miscarriages, or if she or her mate has a known chromosomal abnormality.
None of these tests is 100 percent accurate. You will only know the outcome for sure after your baby is born. Sometimes an inaccurate test result or misinterpretation has led parents to abort a normal baby who was believed to have a defect, or to give birth to a baby with a defect who was believed to be normal.
