title: Chorion villus sampling versus amniocentesis for prenatal diagnosis.
abstract: BACKGROUND
  Amniocentesis 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.
  
  
  OBJECTIVE
  The objective of this review was to assess the safety and accuracy of chorion villus sampling compared to amniocentesis.
  
  
  METHODS
  We searched the Cochrane Pregnancy and Childbirth Group trials register.
  
  
  METHODS
  Randomised trials comparing first trimester chorion villus sampling and second trimester amniocentesis.
  
  
  METHODS
  Trial quality was assessed.
  
  
  RESULTS
  Three 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.
  
  
  CONCLUSIONS
  The 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.
authors.affiliation: Department of Obstetrics and Gynaecology, University of Liverpool, Liverpool, UK, L69 3BX. zarko@liverpool.ac.uk.
authors.forename: Z
authors.initials: Z
authors.lastname: Alfirevic
authors.forename: C M
authors.initials: CM
authors.lastname: Gosden
authors.forename: J P
authors.initials: JP
authors.lastname: Neilson
mesh_terms: D015193:Chorionic Villi Sampling; D005260:Female; D006801:Humans; D011247:Pregnancy; D016032:Randomized Controlled Trials as Topic; D012306:Risk