Amniocentesis. Professor Yves Ville using a needle to perform an amniocentesis test on a pregnant woman. A needle is being inserted through the woman's abdomen into the amniotic sac, which surrounds the foetus. A sample of the amniotic fluid will then be extracted. An ultrasound transducer (lower right) is being used to obtain a picture (upper centre) of the uterus and of the surrounding area. This helps the doctor guide the needle to the best location. The cells extracted in the fluid will be screened for genetic or chromosomal disorders, such as Down's syndrome.