Procedure-related risk of miscarriage following chorionic villus sampling and amniocentesis

Objective:
The objective of our study was to estimate the procedure-related risks of miscarriage following CVS and amniocentesis in a large unselected screened and to determine whether these risks are consistent with those reported in systematic reviews and meta-analysis.

Methods:
This was a retrospective cohort study undertaken at a large Fetal Medicine Unit in the United Kingdom during the period of January 2009 to May 2018. We included all singleton pregnancies that booked at our unit before 20 weeks after excluding those with multiple pregnancies, major fetal defects, terminations and lost to follow-up. We estimated the risk of miscarriage in those that had a CVS or amniocentesis as well as those that did not have any invasive procedure, to estimate the procedure-related risk as a risk-difference (95% confidence interval [CI]). Univariate and multivariate regression analysis was used to derive odds ratios (OR) (95%CI) and determine which maternal and pregnancy characteristics provided a significant contribution in prediction of miscarriage and whether CVS or amniocentesis provided a significant independent.

Results:
During the study period, there were 45,120 singleton pregnancies, including 1,546 that had an invasive procedure. We excluded 1,429 pregnancies (3.2%), due to fetal defects, termination of pregnancy or those with missing outcomes. In pregnancies that underwent CVS, the risk of miscarriage was 1.5% (13/861), compared to 1.2% (476/39,152) in pregnancies that did not have a procedure (p=0.437). In pregnancies that underwent an amniocentesis, the risk of miscarriage was 0.8% (3/375), compared to 1.2% (491/42,463) in those that did not (p=0.520). Univariate and multivariate regression analysis demonstrated that there was no significant prediction to the risk of miscarriage from CVS (p=0.399; p=0.592, respectively) or amniocentesis (p=0.543; p=0.550, respectively). The risk of procedure-related loss attributed to CVS was 0.29% (95%CI: -0.53-1.12) and that following amniocentesis was -0.36% (95%CI: -1.26-0.55), which was not significantly different from those that did not have any procedure.

Conclusion:
The procedure-related risks of miscarriage following CVS and amniocentesis are considerably lower than currently quoted. The estimates of risks based on our study are 0.29% for CVS and -0.36 for amniocentesis.