mRNA COVID‐19 vaccination early in pregnancy and the risk of spontaneous abortion in an international pregnancy registry

Abstract Purpose mRNA COVID‐19 vaccines are used in pregnant populations whether advertently or inadvertently. However, evidence on the safety of these vaccines during pregnancy is limited. The objective of this study is to evaluate the effect of BNT162b2 (Pfizer‐BioNTech) and mRNA‐1273 (Moderna) vaccination during the first 20 weeks of gestation on the risk of spontaneous abortion (SAB). Methods All pregnant women who received at least one dose of BNT162b2 or mRNA‐1273 and enrolled in the COVID‐19 Vaccines International Pregnancy Exposure Registry (C‐VIPER) were prospectively followed from enrollment until 20 weeks of gestation, SAB, or loss to follow‐up. Baseline demographics, vaccination information, and pregnancy outcomes were collected via monthly online self‐administered questionnaires, vaccination certificates, and medical records. Life tables were used to calculate the cumulative risk of SAB. Cox regression was used to estimate the hazard ratio (HR) comparing the two vaccines groups stratified by country of residence and gestational age at enrollment. Results Among 6840 participants who received at least one dose of BNT162b2 or mRNA‐1273 at any time in pregnancy between Jan‐Sep, 2021, 2129 met the inclusion criteria (1576 received BNT162b2 and 553 mRNA‐1273). The two groups were balanced in terms of baseline characteristics. There were 37 SABs, with an overall 13.4% estimated cumulative risk by 20 weeks of gestation, which is similar to the expected risk in the population. The HR of SAB comparing mRNA‐1273 to BNT162b2 was 1.46 (95% CI: 0.66, 3.22). Conclusion The C‐VIPER data show no evidence that mRNA COVID‐19 vaccines increase the risk of SAB.