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 (