During your pregnancy, your doctor may want to do some genetic tests to test for birth defects or chromosomal abnormalities. We have listed the most common tests and their descriptions for your use. Ask your doctor for more information on these procedures.
Between 15 and 18 weeks, your doctor may want to perform a test to determine the level of alpha-fetoprotein (AFP) in your blood. AFP is a substance normally produced by your growing baby. In AFP testing, a blood sample taken from a vein in your arm is analyzed. If the test shows that the AFP level is higher or lower than normal, further tests will be done to confirm or rule out fetal problems.
The analysis of AFP levels can indicate a twin pregnancy, determine the presence of any neural tube defects (when the brain or spinal cord is not forming properly) abdominal wall defects, or help diagnose Down Syndrome.
Human chorionic gonadotropin (HCG)
HCG is commonly measured in your blood and urine to detect pregnancy. It can also help detect Down Syndrome.
Earlier in pregnancy, this measurement can be used along with maternal age, AFP, and HCG to help in the prediction of Down syndrome.
Chorionic villus sampling (CVS)
CVS is a prenatal test that can often detect genetic abnormalities and chromosomal disorders. This test may be recommended by your doctor when you are at advanced maternal age or are at a high risk for genetic abnormalities. CVS involves inserting a needle or catheter into the abdomen or vagina to extract a small sample of placental tissue cells (chorionic villus).
Although a bit invasive, a primary advantage of a chorionic villus sampling is that the procedure can be performed between the 10th and 12th weeks of pregnancy, earlier than an amniocentesis.
An amniocentesis is routinely performed on women between the 15th and 20th weeks of pregnancy who are at risk for genetic disorders, including women who are over age 35. The procedure helps determine chromosomal and genetic disorders and certain birth defects with the extraction and analysis of amniotic fluid.
An amniocentesis is a procedure that involves inserting a long, thin needle through the mother’s abdomen into the amniotic sac to extract a small sample of the amniotic fluid for examination. The amniotic fluid contains cells shed by the fetus. The cell chromosomes are then analyzed for any abnormalities. This test also shows you the sex of your baby. There is a slight risk of miscarriage when undergoing this procedure.
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