• Z Alfirevic, C M Gosden, and J P Neilson.
• Department of Obstetrics and Gynaecology, University of Liverpool, Liverpool, UK, L69 3BX. zarko@liverpool.ac.uk.
• Cochrane Db Syst Rev. 2000 Jan 1; 1996 (2): CD000055CD000055.

BackgroundAmniocentesis test results are usually available only after 18 weeks gestation. Chorion villus sampling (CVS) may be performed transabdominally or transvaginally, usually between 10 and 12 weeks gestation.ObjectivesThe objective of this review was to assess the safety and accuracy of chorion villus sampling compared to amniocentesis.Search StrategyWe searched the Cochrane Pregnancy and Childbirth Group trials register.Selection CriteriaRandomised trials comparing first trimester chorion villus sampling and second trimester amniocentesis.Data Collection And AnalysisTrial quality was assessed.Main ResultsThree studies involving over 9000 women were included. The trials were generally of good quality. Compared to amniocentesis, chorion villus sampling was associated with more sampling and technical failures, and more false positive and false negative results. Pregnancy loss was more common after chorion villus sampling (odds ratio 1.33, 95% confidence interval 1.17 to 1.52). There is a suggestion (though not statistically significant) of an increase in stillbirths and neonatal deaths following chorion villus sampling. Maternal complications were uncommon.Reviewer's ConclusionsThe increase in miscarriages after chorion villus sampling compared to amniocentesis appear to be procedure related. Second trimester amniocentesis appears to be safer than chorion villus sampling. The benefits of earlier diagnosis with chorion villus sampling must be set against the greater risk of pregnancy loss.

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