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a needle is inserted through the abdomen into the fluid around the baby and a small amount of amniotic fluid is withdrawn.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 pregnant person can have a miscarriage at this time of pregnancy, but, if a pregnant person has an amniocentesis, this chance is increased.
While studies have demonstrated different numbers, the chance 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.