CVS provides more genetic and biochemical information than amniocentesis and can be performed earlier in pregnancy and with quicker results. Yet CVS carries a slightly higher risk of damage to the baby than amniocentesis does. So, this higher-yield-higher-risk procedure demands even greater responsibility in making the decision to have the test.
CVS is usually performed between the eighth and twelfth week after the last menstrual period. It is most beneficial when your doctor needs a faster decision than could be obtained by amniocentesis.
There are two methods of performing CVS—transabdominal and transcervical, depending on the safest in your pregnancy. Both approaches depend on ultrasound and results are usually available within 48 hours to one week.
- Transabdominal – a needle is inserted through the abdomen into the uterus to obtain a small amount of tissue from the chorionic villi (finger-like projections of tissue that surround the baby in the early weeks and ultimately form the placenta).
- Transcervical – a catheter is inserted through the vagina and cervix and into the uterus near where the placenta is forming.
Even though CVS provides information earlier in pregnancy than amniocentesis, it carries a risk of miscarriage that is 2 to 4 times higher, depending on the expertise of the physician. Vaginal bleeding frequently occurs following CVS. Studies also suggest a possible increased risk of limb deformities, and CVS may cause a decrease in the amniotic fluid production.