Amniocentesis (sometimes called amnio) is a test which can tell for sure if your baby has Down syndrome or trisomy 18. Sometimes it is used to tell if your baby has an open neural tube defect.
The test is usually done between 15 and 22 weeks of pregnancy.
Using ultrasound, a needle is inserted through the abdomen into the fluid around the baby and a small amount of amniotic fluid is withdrawn. The needle does not touch the baby.
Any woman can have a miscarriage at this time of pregnancy, but, if she has an amniocentesis, this risk is increased an extra 1 in 400 (0.2%). New studies have recently shown that the risk of miscarriage may be even lower, possibly as low as 1 in 1600 (0.06%).
The results are available in 2-3 weeks. Most times, amniocentesis will show that your baby does not have Down syndrome, trisomy 18 or a neural tube defect. Amniocentesis can not find every condition. Even after a normal result, there is a chance of having a baby with a different condition such as a hole in the heart of mental disability.
For more details, talk to your health care provider about amniocentesis.