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What is prenatal diagnostic testing?

Amniocentesis and chorionic villus sampling (CVS) are tests used to diagnose the fetus's state by analyzing fluid or tissue from the mother's uterus. Both are outpatient procedures that can determine with a high degree of accuracy whether the child of carrier parents is healthy.

Prenatal testing is also used to diagnose chromosomal disorders such as Down syndrome.


Amniocentesis has been widely used to detect genetic and chromosomal abnormalities since the early 1970s. Amniocentesis is performed in the second trimester, typically between the 15th and 18th weeks of pregnancy.

Using ultrasound as a guide, the physician inserts a thin needle into the uterus through the abdomen and draws out a small amount of amniotic fluid, which is then analyzed for evidence of genetic or chromosomal disorders.

Amniocentesis results are usually available in 1 to 3 weeks.

Chorionic villus sampling (CVS)

Chorionic villus sampling (CVS) is a prenatal testing method with accuracy rates comparable to amniocentesis. Unlike amniocentesis, CVS can be performed in the first trimester, between the 10th and 12th weeks of pregnancy, allowing parents to get an earlier diagnosis.

CVS involves analysis of the chorionic villi, which are tiny branchlike projections of the placenta. It can detect the same recessive genetic diseases as amniocentesis.

Using ultrasound as a guide, the physician inserts a catheter or thin needle into the uterus through either the abdomen or the cervix, depending on the position of the placenta. A small sample of the placenta is removed and analyzed for evidence of genetic or chromosomal abnormalities.

Results for CVS take approximately 1 to 3 weeks.

Is prenatal testing safe?

Complications from CVS and amniocentesis are rare. Both procedures carry a very small risk of miscarriage or maternal infection. Studies show the risk is lowest when a highly experienced practitioner performs the tests. A genetic counselor can give you a referral to a physician or medical center with extensive experience in prenatal diagnosis.

Understanding the results of prenatal diagnostic testing

Disease inheritance is complex. Some gene mutations may cause mild symptoms, others severe. Your genetic counselor will analyze your fetal test results and help you understand what they mean.