Introduction: The aim of this paper was to estimate the risk of miscarriage after amniocentesis or chorionic villus sampling (CVS) based on a systematic review of the literature.
Evidence acquisition: A search of Medline, Embase, and The Cochrane Library (2000-2017) was carried out to identify studies reporting complications following CVS or amniocentesis. The inclusion criteria for the systematic review were studies reporting results from large controlled studies (N.≥1000 invasive procedures) and those reporting data for pregnancy loss prior to 24 weeks' gestation. Data for cases that had invasive procedure and controls were inputted in contingency tables and risk of miscarriage was estimated for each study. Summary statistics were calculated after taking into account the weighting for each study included in the systematic review. Procedure-related risk of miscarriage was estimated as a weighted risk difference from the summary statistics for cases and controls.
Evidence snthesis: The electronic search from the databases yielded 2465 potential citations of which 2431 were excluded, leaving 34 studies for full-text review. The final review included 10 studies for amniocentesis and 6 studies for CVS, which were used to estimate risk of miscarriage in pregnancies that had an invasive procedure and the control pregnancies that did not. The procedure-related risk of miscarriage following amniocentesis was 0.35% (95% confidence interval [CI]: 0.07 to 0.63) and that following CVS was 0.35% (95% CI: -0.31 to 1.00).
Conclusions: The procedure-related risks of miscarriage following amniocentesis and CVS are lower than currently quoted to women.