350: Amniocentesis does not increase the risk of miscarriage in patients with positive prenatal screening

Abstract

To estimate the risk of pregnancy loss among prenatal screen positive singleton pregnancies after mid-trimester amniocentesis by experienced practitioners. Screen positive patients in the California Prenatal Screening Program are offered referral to Prenatal Diagnosis Centers (PDC), where they are offered genetic counseling, detailed anatomic ultrasound, and amniocentesis. Pregnancy losses were ascertained via outcome of pregnancy surveys sent to the providers of all screen positive patients. Singleton pregnancies having amniocentesis were compared with those that declined. Cases with chromosome abnormalities or structural birth defects based on PDC visit reports, outcome survey, or California Chromosome Registry report were excluded. Cases that were screen positive for neural tube defects were also excluded based on the difference in amniocentesis acceptance rates in this population. Two-sided confidence intervals for the loss rates in the two groups were calculated. After exclusions, there were 11,478 amniocenteses and 14,475 declines who were screened between April 2009 and December 2012. In the amniocentesis group, there were 80 fetal losses (0.70%, 95% CI 0.54%-0.85%). In the decline group, there were 117 fetal losses (0.81%, 95% CI 0.66%-0.95%). These rates were not significantly different (p=0.84). The probability that any increase in loss rate associated with amniocentesis, if present, is <1/1000 is 0.82, and that any increase is <1/500 is 0.97. The risk of pregnancy loss in a singleton, prenatal screen positive pregnancy after amniocentesis by an experienced practitioner is 1/143 (0.70%), which is equal to the loss rate when amniocentesis is declined in these high-risk pregnancies. There is no evidence that amniocentesis by an experienced practitioner increases the risk of pregnancy loss. The increase in pregnancy loss after amniocentesis is smaller than current estimates.