Observational Studies Show No Evidence That COVID-19 Immunization Causes Spontaneous Abortion

Infection with SARS-CoV-2 during pregnancy is associated with excess risks for preterm birth and other adverse pregnancy outcomes. Among the barriers to immunizing pregnant women against COVID-19 is the fear that immunization might lead to pregnancy loss. Two recent reports address this concern.

In a case-control study from eight large U.S. healthcare systems, investigators identified ongoing pregnancies between 6 and 19 weeks of gestation on the last day of seven consecutive 4-week surveillance periods beginning in December 2020; they also identified spontaneous abortions occurring during each surveillance period. Among more than 100,000 pregnancies, 12.8% ended in spontaneous abortion. COVID-19 vaccines were received within 28 days before 8.6% of spontaneous abortions and before 8.0% of ongoing pregnancies at the end of each surveillance period — a nonsignificant difference.

In another study, researchers analyzed pregnancy outcomes among 2456 women enrolled in a CDC pregnancy registry who were at least 6 weeks pregnant and who had received at least one dose of an mRNA COVID-19 vaccine before conception or before 20 weeks of gestation. The age-standardized risk of spontaneous abortion between 6 and 20 weeks of gestation was 12.8%, which was within the expected risk range based on historical cohorts.