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Spontaneous Abortion Risk Not Increased by COVID-19 mRNA Vaccines

Even though expectant mothers face significant danger from COVID-19, they also are understandably fearful about how vaccination will affect their pregnancies. A new CDC study provides some reassurance. Researchers determined that mRNA vaccinations have no higher risk of spontaneous abortion than typical. Here are more details.

ATLANTA – Women who receive COVID-19 mRNA either shortly before conception or during pregnancy don’t appear to have an outsized risk of spontaneous abortion, according to a new study.

On the other hand, the national Centers for Disease Control and Prevention researchers, infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during pregnancy is associated with increased risks of preterm birth and other adverse maternal and neonatal outcomes.

The research letter published in The New England Journal of Medicine points out that spontaneous abortion – defined as pregnancy loss occurring at less than 20 weeks of gestation --is a common pregnancy outcome affecting 11% to 22% of recognized pregnancies. Data has been limited, however, on how that was affected by COVID-19 vaccination, the authors advise.

The study team analyzed data from the Centers for Disease Control and Prevention (CDC) v-safe Covid-19 vaccine pregnancy registry to determine the cumulative risk of spontaneous abortion from 6 to less than 20 weeks of gestation. Included in the analysis were nearly 2,500 participants with a singleton pregnancy who had received at least one dose of an mRNA Covid-19 vaccine either before conception or before 20 weeks of gestation and who did not have a pregnancy loss before 6 weeks.

Of the participants, 2,022 participants reported ongoing pregnancies at 20 weeks of gestation, 165 participants reported a spontaneous abortion (154 participants before 14 weeks of gestation) and 65 participants with most recent contact during the first trimester could not be reached for second-trimester follow-up, 188 participants completed second-trimester follow-up before 20 weeks of gestation, and 16 participants reported another pregnancy outcome before 20 weeks (induced abortion or ectopic or molar pregnancy).

The women in the study tended to be 30 years of age or older (77.3%), were non-Hispanic White (78.3%), and worked as healthcare personnel (88.8%). Slightly more than half the participants (52.7%) had received the BNT162b2 vaccine (Pfizer–BioNTech) (Table S2).

Results indicate that cumulative risk of spontaneous abortion from 6 to less than 20 weeks of gestation was 14.1% (95% confidence interval [CI], 12.1 to 16.1) in the primary analysis and 12.8% (95% CI, 10.8 to 14.8) in an analysis using direct maternal age–standardization to the reference population.

Researchers report that the cumulative risk of spontaneous abortion increased with maternal age.”In the sensitivity analysis, under the extreme assumption that all 65 participants with most recent contact during the first trimester had a spontaneous abortion, the cumulative risk of spontaneous abortion from 6 to less than 20 weeks of gestation was 18.8% (95% CI, 16.6 to 20.9); after age standardization, the cumulative risk was 18.5% (95% CI, 16.1 to 20.8),” they write.

The study concludes, “As compared with data from two historical cohorts that represent the lower and upper ranges of spontaneous-abortion risk, the cumulative risks of spontaneous abortion from our primary and sensitivity analyses were within the expected risk range.”