Miscarriage after SARS‐CoV‐2 vaccination: A population‐based cohort study

Abstract

ObjectiveTo evaluate the risk of miscarriage following SARS‐CoV‐2 vaccination, while accounting for the competing risk of induced abortion.DesignPopulation‐based cohort study.SettingOntario, Canada.ParticipantsWomen aged 15–50 years with a confirmed pregnancy at ≤19 completed weeks’ gestation.MethodsExposure to first SARS‐CoV‐2 vaccination, handled in a time‐varying manner, was defined as (i) unvaccinated, (ii) remotely vaccinated >28 days before the estimated conception date or (iii) recently vaccinated ≤28 days before conception and up to 120 days after conception.Main outcome measuresThe outcome was miscarriage, occurring between the estimated date of conception and up to 19 completed weeks of pregnancy. Fine‐Grey hazard models, accounting for the competing risk of induced abortion, generated hazard ratios (aHR), adjusted for socio‐demographic factors, comorbidities, and biweekly periods.ResultsIncluded were 246 259 pregnant women, of whom 34% received a first SARS‐CoV‐2 vaccination. Miscarriage occurred at a rate of 3.6 per 10 000 person‐days among remotely vaccinated women and 3.2 per 10 000 person‐days among those recently vaccinated, in contrast to a rate of 1.9 per 10 000 person‐days among unvaccinated women, with corresponding aHR of 0.98 (95% confidence interval [CI] 0.91–1.07) and 1.00 (95% CI 0.93–1.08).ConclusionsSARS‐CoV‐2 vaccination was not associated with miscarriage while accounting for the competing risk of induced abortion. This study reiterates the importance of including pregnant women in new vaccine clinical trials and registries, and the rapid dissemination of vaccine safety data.

Miscarriage after SARS‐CoV‐2 vaccination: A request to report more details of the regression models and analyses

“…Dear Dr. Papageorghiou, In the paper 'Miscarriage after SARS-CoV-2 vaccination: A population-based cohort study', 1 Velez et al compare miscarriage rates and induced abortion rates between vaccinated and unvaccinated women, from conception and up to 19 complete weeks (140 days) of pregnancy in Ontario, Canada, including women with a conception day between December 2020 and December 2021. Vaccinated women were divided into 'remotely vaccinated', who received the first vaccine dose earlier than 28 days before conception, and 'recently vaccinated', who received the first vaccine dose from 28 days before conception and up to 120 days after conception.…”