Prenatal Diagnostic Procedures
Testing During Pregnancy
Prenatal diagnostic procedures are used to obtain genetic information about the fetus. These tests are diagnostic, meaning they can determine if the fetus has a chromosome abnormality or a specific genetic disease. Below are descriptions of several diagnostic procedures that are performed during pregnancy.
Chorionic Villus Sampling (CVS)
Chorionic villus sampling (CVS) is a prenatal diagnostic procedure. CVS is performed in the first trimester (10 to 13 weeks in pregnancy) by using a long thin straw-like tube inserted into the cervix and guided by ultrasound into the placenta. A syringe is attached to the tube and the chorionic villi, (placental tissue) which have the same genetic make up as the fetus, is sampled. The chorionic villus tissue can be analyzed for chromosome abnormalities such as Down syndrome. Biochemical or DNA analysis can be performed on the chorionic villus specimen to diagnose specific inherited conditions such as cystic fibrosis, Tay Sachs disease or sickle cell anemia. This procedure is performed under the guidance of ultrasound. Chromosome results are usually available within two weeks.
Amniocentesis
Amniocentesis is usually performed in the second trimester of pregnancy (between the 15th and 20th weeks). During Prenatal Diagnostics testing, an amniocentesis needle is guided by ultrasound into the sac of fluid surrounding the fetus and 3 to 4 tablespoons of amniotic fluid is obtained. Chromosome analysis for Down syndrome and biochemical analysis for neural tube defects such as spina bifida are the most common tests performed on the amniotic fluid. Like CVS, other types of biochemical and DNA analysis can be performed on the amniotic fluid for specific inherited conditions. Chromosome results are usually available within two weeks.
Cordocentesis
Cordocentesis is a procedure used to obtain a sample of fetal blood from the umbilical cord of the fetus. This procedure is performed under the guidance of ultrasound, usually between the 18th to 23rd week of pregnancy. Cordocentesis also can be performed throughout the later second and third trimester. Chromosome analysis, biochemical analysis, viral studies and blood cell counts can be performed from the blood obtained from the cordocentesis. Results are usually available within a few days.
