CVS is a prenatal test typically performed between 10-14 weeks of pregnancy. It is the withdrawal of a small amount of chorionic tissue (part of the placenta), by either a catheter through the cervix or a needle inserted into the abdomen. The procedure is performed under ultrasound guidance. CVS can detect chromosome abnormalities, such as aneuploidy, rearrangements, and major duplications/deletions, with 99.6% – 99.8% accuracy. The risk of miscarriage associated with the procedure is 1/200 (0.5%).

Amniocentesis is typically performed between 15-23 weeks of pregnancy. In this procedure, a small amount of amniotic fluid (fluid surrounding the unborn baby) is withdrawn from the uterus by a thin needle through the abdomen. Like the CVS, the procedure is done under ultrasound guidance and can detect chromosome abnormalities, such as aneuploidy, large duplications/ deletions, and large rearrangements, with 99.6%-99.8% accuracy. The procedure can also detect open neural tube defects (spina bifida and anencephaly) and abdominal wall defects with approximately 95% accuracy. The risk of miscarriage associated with the procedure is 1/300 (0.3%).