Amniocentesis is the procedure by which a small amount of fluid is drawn from the amniotic sac in order to perform diagnostic genetic tests to examine the health of the fetus. The amniotic fluid after the 16th week of the pregnancy when amniocentesis is performed, is basically fetal urine, containing cells from the bladder, the mouth, the lungs and the skin of the fetus. Therefore the amniotic fluid is an excellent source of fetal genetic material that can be used for any genetic analysis.

The procedure is performed since the 1960s. It was initially used to measure cholerythrine in pregnancies complicated by Rhesus disease and later to look for chromosomal abnormalities. Over the decades the technique has evolved and the procedure is now performed under direct ultrasound guidance.

Large studies published in the last decade have addressed the issue of the safety of the procedure confirming a very low complication rate. Possible complications include miscarriage (occurring in about 1-3 per 1000 procedures) and leakage of amniotic fluid, usually self-contained without any consequences.