Low-risk amniocentesis in the third trimester under ultrasound control.

Amniocentesis was performed under ultrasound control on 501 third-trimester gravidae out of the 509 referred. Eight patients were excluded based on the ultrasound examination, since practically no amniotic fluid could be detected. Ultrasound was used to find a pocket of amniotic fluid in which the puncture would carry no risk to the foetus. The puncture was made immediately after the examination, on the same examination table. In 17% of cases the puncture was made in the lower uterine segment behind the foetal neck. A diagnostic sample of the amniotic fluid was obtained in 87.4% of cases. In the other 12.6%, the sample either could not be obtained (7.8%) or contained blood (4.8%). In 1.8% of cases the membranes ruptured within 24 hours of the puncture. In no case could any damage be shown either to the foetus or to the placenta, nor were there any signs of intrauterine infection.