Amniocentesis (also referred to as amniotic fluid test or AFT) is a medical procedure used in prenatal diagnosis of chromosomal abnormalities and foetal infections, and also for sex determination, in which a small amount of amniotic fluid, which contains foetal tissues, is sampled from the amniotic sac surrounding a developing foetus, and then the foetal DNA is examined for genetic abnormalities. Amniocentesis (or another procedure, called chorionic villus sampling (CVS)) can diagnose these problems in the womb. Amniocentesis is performed when a woman is between 14 and 16 weeks gestation.