Peripartum Outcomes Following COVID-19 Vaccination in Late Pregnancy: Findings from a Population-Based Retrospective Cohort Study in Ontario, Canada

ABSTRACT

Objectives: Evaluate peripartum outcomes following COVID-19 vaccination during pregnancy. Methods: Ontario population-based retrospective cohort between December 14, 2020 and September 30, 2021 using linkage of provincial birth registry and COVID-19 immunization databases. Poisson regression was used to generate risk ratios (RR) and 95% confidence intervals (CI), adjusted for temporal, socio-demographic, and clinical factors using propensity scores. Obstetric (postpartum hemorrhage, chorioamnionitis, cesarean birth) and newborn (NICU admission and 5-minute Apgar<7) outcomes were compared for those who received ≥1 dose of COVID-19 vaccine during pregnancy with 2 unexposed groups—Group 1 individuals vaccinated postpartum, Group 2 never vaccinated. Results: Among 97 590 individuals, 22 660 (23%) received ≥1 dose of vaccine during pregnancy (64% received dose 1 in 3rd trimester). Compared with those vaccinated postpartum, we found no increased risks of postpartum hemorrhage (aRR 0.91, 95% CI 0.82–1.02);chorioamnionitis (aRR 0.92, 95% CI 0.70–1.21);or cesarean (aRR 0.92, 95% CI 0.89–0.95) following COVID-19 vaccination, nor any increased risk of NICU admission or 5-minute Apgar <7. All findings were similar when compared with individuals who did not receive COVID-19 vaccination at any point. We did not observe any difference according to vaccine product, number of doses received during pregnancy, or trimester of dose 1. Conclusions: As of late 2021, there is limited evidence from comparative studies in large populations on outcomes following COVID-19 vaccination during pregnancy. Our study of births up to September 30, 2021 did not identify any increased adverse peripartum outcomes associated with later pregnancy COVID-19 vaccination. Once more individuals vaccinated earlier in pregnancy deliver, we will report on other important obstetric and perinatal outcomes. Keywords COVID-19 vaccine;pregnancy;epidemiology