Ultrasound is used to guide a needle through the abdomen into the fluid-filled sac. It is recommended for women who are over age 35 at the time of delivery and when there is a family history of genetic disorders. The procedure is usually performed at around 15-19 weeks gestation. There is a 1 in 200 chance for a complication to occur. Complications include miscarriage, infection and rupture of membranes.
Results are available in two weeks.
Amniocentesis is also performed later in gestation to assess fetal lung maturity. Like amniocentesis, it is an accurate method of prenatal diagnosis. CVS, however, can detect genetic or chromosomal abnormalities earlier in pregnancy. It is performed between the 10th and the 12th week of pregnancy. Under ultrasound guidance, a thin plastic tube is inserted through the cervix into the placenta and a villus sample is removed.