Fetal loss rate after chorionic villus sampling and amniocentesis: an 11-year national registry study.

OBJECTIVE To assess the fetal loss rate following amniocentesis and chorionic villus sampling (CVS). METHODS This was a national registry-based cohort study, including all singleton pregnant women who had an amniocentesis (n = 32 852) or CVS (n = 31 355) in Denmark between 1996 and 2006. Personal registration numbers of women having had an amniocentesis or a CVS were retrieved from the Danish Central Cytogenetic Registry, and cross-linked with the National Registry of Patients to determine the outcome of each pregnancy. Postprocedural fetal loss rate was defined as miscarriage or intrauterine demise before 24 weeks of gestation. RESULTS The miscarriage rates were 1.4% (95% CI, 1.3-1.5) after amniocentesis and 1.9% (95% CI, 1.7-2.0) after CVS. The postprocedural loss rate for both procedures did not change during the 11-year study period, and was not correlated with maternal age. The number of procedures a department performed had a significant effect on the risk of miscarriage. In departments performing fewer than 500 amniocenteses, the odds ratio for fetal loss was 2.2 (95% CI, 1.6-3.1) when compared to departments performing more than 1500 procedures during the 11-year period. For CVS the risk of miscarriage was 40% greater in departments performing 500-1000 and 1001-1500 as compared to those performing more than 1500 procedures. CONCLUSIONS The miscarriage rates (i.e. spontaneous loss and procedure-related loss) after amniocentesis and CVS were 1.4% and 1.9%, respectively. This difference may be explained by the difference in gestational age at the time of the procedures. The miscarriage rate was inversely correlated with the number of procedures performed in a department.