re birth for congenital adrenal hyperplasia. Biotin dependence and MMA (methylmalonic acidemia), both life threatening, can be detected and treated in the womb.
Today there are tests for about 450 genetic diseases. However, the majority of these tests remain available only to research laboratories and are offered only to family members of someone who has been diagnosed with a genetic condition. About 50 genetic tests are available for clinical use (Gazis-Sax, 1997).
The most commonly used methods of prenatal testing are amniocentesis, chorionic villus sampling (CVS), maternal blood tests, ultrasound, and umbilical cord assessment (Health Net Demonstration Project, 1998). Amniocentesis involves taking a sample of amniotic fluid and analyzing it to detect the presence of various genetic defects (Fuchs, 1990).
The procedure is usually done in the fifteenth or sixteenth week of pregnancy and takes two to four weeks to receive results (Tarbor, Philip, Madsen, Bang, Obel & Norgaard-Pedersen, 1986). According to Tarbor and associates (1986), amniocentesis has a risk of miscarriage and is only recommended for women who are at least 35 years of age or who are known carriers of Tay-Sachs or sickle cell disease, or couples who have a family history of conditions such as Down Syndrome, spina bifida, Rh disease, or muscular dystrophy.
Chorionic villus sampling (CVS) consists of taking issue from the end of one or more villi---hairlike projections of the membrane around the embryo---which are made up of fetal cells (Rhoads & Associates, 1989). The cells are then tested for the presence of various conditions. CVS carries a somewhat higher risk of miscarriage than does amniocentesis (Rosenthal, 1991).
The maternal blood test, a very frequently used prenatal procedure, is commonly performed between the fourteenth and twentieth week of pregnancy---the blood being tested for its amount of alpha fetoprotein (AFP). According to ...