With pregnancy comes an onslaught of tests ? from ultrasounds to blood work ? that regularly happen throughout your nine months. One test that can come up in the second trimester is amniocentesis.
What is amniocentesis"
Amniocentesis (?amnio? for short) is a prenatal medical test that involves a very thin, long needle being inserted through the belly into your uterus to remove a small amount of amniotic fluid from the pool of fluid your baby is sitting in. ?It?s a simple procedure that only takes a minute or two to perform,? says Ken Lim, division head of Maternal Fetal Medicine at BC Women’s Hospital & Health Centre in Vancouver and the Provincial Health Services Authority.  Amniocentesis is performed by a doctor, usually, one who specializes in maternal-fetal medicine. The doctor withdraws a small amount, typically about two to three tablespoons, or 30 to 40 cubic centimeters, says Lim. To put that in context, the total amount of amniotic fluid in the uterus ranges from 250 to 500 cubic centimetres, as it varies depending on where you are in your pregnancy. The fluid replenishes hours later, explains Lim. 
The amniotic fluid can give doctors genetic information about your baby, as the liquid contains cells that are representative of your baby. After the sample is taken, the fluid is sent to a lab, where it can be analyzed to directly look for genetic disorders such as Down syndrome or cystic fibrosis or indirectly for birth defects such as spina bifida (...