Amniocentesis is a procedure performed in our office under ultrasound guidance.  A small sample of amniotic fluid, which is the fluid that the baby is floating in, is removed and sent for testing.

An amniocentesis is available at different stages of pregnancy and for different reasons.  An early amniocentesis is done between 12 and 14 weeks.  The most traditional timing for an amniocentesis is between 15 and 22 weeks.  In general, amniocentesis performed during these times is done to detect chromosomal abnormalities (such as Down syndrome) and open neural tube defects (also known as spina bifida).  If indicated, it may also be possible to perform genetic DNA testing on the sample.  Amniocentesis may also be performed in the third trimester to determine fetal lung maturity. 

Amniocentesis does involve a risk for miscarriage.  An amniocentesis performed within 14 weeks of pregnancy or less has a 1 in 100 (1%) risk, while an amniocentesis performed at 15 weeks of pregnancy and after has a 1 in 300 (0.3%) risk or less.