Altogether 10 reports on the safety of chorionic villus sampling, either by the transcervical (TC) or the transabdominal (TA) approach, were reviewed and combined with our own data. After discussion of how unintended fetal loss rates are best estimated, the excess total fetal loss after TC and TA compared with amniocentesis were estimated to be 1.70% (+/- 0.65%) and practically zero (+/- 1.0%), respectively (standard errors in parentheses). The absolute risk of unintended loss after TC is +2.7% (+/- 0.7%) and after TA 1.0% (+/- 1.0%). These estimates are still too uncertain to allow precise weighting of benefits and human costs. A uniform style of reporting studies in this area is proposed.