Some tests can detect genetic abnormalities before birth. By learning about these problems before birth, you can help plan your child’s health care in advance, and in some cases even treat the disorder while the baby is still in the womb.
Amniocentesis
- With amniocentesis, the doctor inserts a thin needle through the pregnant woman’s abdominal wall into the uterus. A small sample of amniotic fluid is taken from the sac surrounding the fetus. When the fluid is analyzed in the laboratory, it can check for serious genetic and chromosomal disorders, such as Down syndrome. For genetic studies, amniocentesis is usually performed during the second trimester (between the fifteenth and twentieth weeks of pregnancy), although it may be done later (typically after the thirty-sixth week) to test whether the baby’s lungs are developed enough for birth. Results of most amniocentesis tests are available within about two weeks.
Chorionic Villus Sampling (CVS)
- With chorionic villus sampling (CVS), a long, slender needle is inserted through the abdomen to remove a small sample of cells (called chorionic villi) from the placenta. Or a catheter (a thin plastic tube) is placed into the vagina and then inserted through the cervix to take cells from the placenta. This sample is then analyzed in the laboratory. CVS is usually performed earlier during the pregnancy than amniocentesis, most often between the tenth and twelfth week of pregnancy. The test results are available within one to two weeks.
Both amniocentesis and CVS are considered accurate and safe procedures for prenatal diagnosis, although they pose a small risk of miscarriage and other complications. You should discuss both the benefits and the risks with your doctor and, in some cases, with a genetic counselor.
Non-Invasive Prenatal Testing (NIPT)
- During pregnancy, some of the baby’s genetic information (DNA) crosses into the mother’s bloodstream. Non-invasive prenatal testing (NIPT) analyzes this DNA to check if the baby has a higher chance of having certain chromosomal disorders. A blood sample is taken from the mother (not from the baby) usually after the tenth week of pregnancy. Because NIPT only involves a blood draw from the mother, the pregnancy is not at risk for miscarriage or other complications. The test results are available within one to two weeks. NIPT is a screening test which means that an amniocentesis or CVS may be offered to confirm results.