Amniocentesis (sometimes called amnio) is a test which can tell for sure if your baby has Down syndrome or trisomy 18.
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a needle is inserted through the abdomen into the fluid around the baby and a small amount of amniotic fluid is withdrawn.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.
While studies have demonstrated different numbers, the risk of miscarriage associated with amniocentesis typically quoted is 1 in 400 (0.2%).
The results are available in 2-3 weeks. Most times, amniocentesis will show that your baby does not have Down syndrome or trisomy 18. 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.