Association of COVID-19 Vaccination in Pregnancy With Adverse Peripartum Outcomes

PURPOSE OF THE STUDY: To evaluate the association between coronavirus disease 2019 (COVID-19) vaccination during pregnancy and peripartum outcomes. STUDY POPULATION: This study included all pregnancy records in the Canadian birth registry (Better Outcomes and Network Ontario) with a birth date or expected due date on or after December 14, 2020. The birth registry was linked with records within the provincial COVID-19 immunization database (COVaxON) up to September 30, 2021. The study included 97 590 persons who gave birth during this period with the majority of participants being vaccinated in the third trimester. Demographically, those vaccinated during pregnancy were more similar to those vaccinated after pregnancy than those never vaccinated. METHODS: This was a population-based retrospective cohort study using data provided in the birth registry and immunization database. COVID-19 vaccination was considered to have occurred during pregnancy if 1 or more doses were administered between the estimated date of conception (estimated by adding 14 days to the last menstrual period date) up to 1 day before birth with 23% of participants meeting this criteria. Individuals that were unvaccinated during pregnancy (77% of total participants) were divided into 2 comparison groups: (1) those vaccinated after pregnancy (46%) and (2) those with no record of any COVID-19 vaccination (31%) by September 30, 2021. Measured obstetric outcomes included postpartum hemorrhage, chorioamnionitis, cesarean delivery, and emergency cesarean delivery. Newborn outcomes included NICU admission and low newborn 5-minute Apgar score (<7). Poisson regression was used to calculate unadjusted risk differences and risk ratios and propensity score methods were used to account for potential confounding bias. RESULTS: Compared with those vaccinated after pregnancy, there was no significant association between COVID-19 vaccination during pregnancy and obstetric outcomes (postpartum hemorrhage, chorioamnionitis, cesarean delivery, or emergency cesarean delivery). However, rates of adverse newborn outcomes were lower among those born to individuals vaccinated during pregnancy with a lower risk of both NICU admission and low 5-minute Apgar scores. When compared with those that were not vaccinated at any time, participants vaccinated during pregnancy had no increased risks of any of the outcomes. In fact, there was a lower risk of emergency cesarean delivery and NICU admissions. Finally, when stratifying participants vaccinated during pregnancy by number of doses received, vaccine product, or trimester of vaccine dose 1, there was no statistically significant changes in study outcomes. CONCLUSIONS: Overall, vaccination was not associated with an increased risk of postpartum hemorrhage, chorioamnionitis, cesarean delivery, NICU admission, or low 5-minute Apgar score. In fact, vaccination during pregnancy may be protective to neonates with decreased risk of NICU admissions and low Apgar scores. These results are consistent with research regarding other vaccines such as influenza and pertussis that show no significant association with adverse maternal, fetal, or neonatal outcomes.