It is common for every pregnant woman to wonder whether her baby is healthy. In situations where the pregnancy may be at increased risk for chromosomal abnormalities or certain other conditions, genetic counseling and chorionic villus sampling (CVS) may be recommended.
The most common reasons to consider genetic counseling are:
- Increased risk for chromosomal defects based on first trimester screening, an abnormal early pregnancy sonogram, or maternal age.
- A family history or prior baby affected by certain genetic disorders, such as cystic fibrosis or sickle cell anemia.
CVS is a procedure that involves obtaining a small fragment of the placenta (villous), via a tiny flexible catheter that is inserted through the cervix or via a needle inserted through the abdomen. The pathway (transcervical or transabdominal) is dependent upon the location of the placenta. The CVS sample is sent to the genetics lab where the test(s) appropriate for the woman’s risk can be performed. Conditions that can be diagnosed via CVS include chromosomal problems (e.g. Down syndrome), inherited conditions (e.g. Tay-Sachs and sickle-cell anemia) and conditions that are influenced by the sex of the baby (e.g. hemophilia).
CVS is performed in the ultrasound unit at San Diego Perinatal Center. The procedure is ultrasound-guided and is usually performed at 11 ½ to 12 ½ weeks gestation. Under unusual circumstances it may be performed later, but a CVS is never performed at this facility prior to 10 weeks gestation. Currently available information indicates that the risk of miscarriage after a CVS is 1 in 175 to 200.
After the CVS procedure, the woman goes home and should have reduced activity for 24 hours (i.e. no working, exercising, or cooking). She can then resume her normal activity. Following the procedure, a woman may have some mild cramping, but should not have severe cramping, fever or heavy bleeding. The CVS test results are typically available within 10 to 14 days. It is recommended that a person having a CVS have a follow-up, high-resolution ultrasound at 17 to 18 weeks gestation and consider expanded AFP testing at 16 to 18 weeks gestation.
The major advantage of CVS relative to amniocentesis is that the CVS procedure can be done at 11 ½ to 12 ½ weeks of pregnancy as compared to 15 to 16 weeks for amniocentesis. A disadvantage of CVS relative to amniocentesis is that AFP testing is not done on the CVS specimen.