Risk of heavy menstrual bleeding following COVID-19 vaccination: A nationwide case-control study

Background: COVID-19 vaccination has been inconsistently associated with an increased risk of heavy menstrual bleeding in previous studies. This study aimed to assess the risk of heavy menstrual bleeding requiring hospital care following COVID-19 vaccination according to the number of doses received and the time elapsed since vaccination. Methods: Using comprehensive data of the French National Health Data System, we carried out a case-control study. Non-pregnant 15-50 years old women who had a hospital discharge diagnosis of heavy menstrual bleeding between May 12, 2021, and August 31, 2022 (cases) were randomly matched to up to 30 controls of same age, place of residence, social deprivation index, and contraceptive use profile at the date of case hospital admission (index date). Conditional logistic regression models were used to estimate the risk of hospital care for heavy menstrual bleeding associated with primary or booster doses and delay since last COVID-19 vaccination at index date, adjusting for socio-demographic characteristics, comorbidities, healthcare use indicators, and recent SARS-CoV-2 infection. Results: A total of 4610 cases and 89,375 matched controls were included (median age, 42 years). Compared to unvaccinated women, the risk of hospital care for heavy menstrual bleeding was increased in those having received a last dose of primary vaccination in the preceding 1-3 months (Odds Ratio, 1.20 [95% confidence interval, 1.07-1.35]). This association was marked among women residing in the most deprived municipalities (1.28 [1.07-1.52]) and those who were not using hormonal contraception (1.28 [1.11-1.48]). Assuming a causal relationship, a total of 103 cases [54-196] were estimated to be attributable to primary vaccination in France. Conclusion: These findings provide evidence of an increased risk of heavy menstrual bleeding during the threemonth period following primary COVID-19 mRNA vaccination. No increased risk was found beyond 3 months after primary vaccination nor following booster doses.