Amniocentesis is an optional test that is usually performed during the 15th-20th weeks of pregnancy. Doctors take a small sample of amniotic fluid that surrounds the baby that can then be tested for chromosomal abnormalities in the fetus. There is a small (around 0.5%) risk of miscarriage as a result of the procedure which involves the insertion of a thin, hollow needle into the amniotic sac.
This is a companion discussion topic for the original article at https://patient.info/news-and-features/amniocentesis-what-is-it-what-are-the-risks-and-do-you-need-this-test