A British study compared two methods of detecting genetic abnormalities in the foetus: amniocentesis (extraction of the fluid that bathes the foetus) versus sampling the chorionic villi (CVS), which forms part of the developing placenta. Amniocentesis can prompt a miscarriage. Severe limb deformities were found in four babies carried by women who had undergone CVS. In the UK more than 1,000 such tests are conducted each year.
In the USA, amniocentesis is can trigger a miscarriage in about one in 200 to one in 400 cases.