Multicentre randomised clinical trial of chorion villus sampling and amniocentesis. First report. Canadian Collaborative CVS-Amniocentesis Clinical Trial Group.

2787 women who were aged 35 years or more at expected date of delivery were randomised to chorionic villus sampling (CVS) at 9-12 weeks gestation or amniocentesis at 15-17 weeks for the detection of a chromosomal abnormality in the fetus. 396 women were excluded after randomisation because of a non-viable fetus, a multiple pregnancy, or infection or because the pregnancy was too far advanced (more than 12 completed weeks). Among all women eligible at the time of the first study procedure there were 89/1169 (7.6%, 95% confidence interval [CI] 6.2-9.3%) total losses (spontaneous and induced abortions and late losses) in the CVS group and 82/1174 (7.0%, CI 5.6-8.6%) in the amniocentesis group for an excess of 0.6% for those women undergoing CVS, with a tendency to later losses in the CVS group. Approximate 95% CIs indicate that this difference is most unlikely to be greater than 2.7%. Mean birthweights for each week of gestation were similar in both groups, with no evidence of excess small-for-gestational age babies in the CVS group. The proportion of preterm births were similar in both groups. Perinatal mortality was greater in the CVS group, the greatest imbalance being beyond 28 weeks. Preliminary analysis has not disclosed an obvious recurrent event in the CVS group which might explain a cause-and-effect relationship for these late fetal losses. There is no evidence of any excess intrauterine growth retardation babies in the CVS group. Maternal morbidity was similar in both groups. 103/1037 (9.9%) women eligible for CVS had a further amniocentesis; 32 of these second procedures were needed to complete the cytogenetic diagnosis. More problems such as confined mosaicism and maternal cell contamination occurred in the interpretation of the CVS samples, but these were clarified by amniocentesis when appropriate.

RCT Entities:   Population Interventions Outcomes