Background: As reports of abnormal uterine bleeding (AUB) following COVID-19 vaccination have emerged, there has been a growing concern regarding the potential risks associated with AUB.
Objectives: To assess the association between COVID-19 vaccination and the risk of AUB related to frequent and irregular menstruation, or bleeding in women
Methods: We used a database that linked nationwide COVID-19 registry data, which included information on COVID-19 infection and vaccination, with the National Health Insurance Service claims database in South Korea. We included women aged 16-64 who received their first vaccine dose before October 31, 2021 and were newly diagnosed with AUB in inpatient or outpatient settings within 120 days after receiving the 1st dose. The AUB patients were identified through the presence of ICD-10-CM diagnosis codes and related procedure codes such as ultrasonography, biopsy of endometrium, and vaginal treatment using speculum. We excluded patients who had a history of AUB, structural anomalies proposed by Federation of Gynecology and Obstetrics (FIGO) classification, cancer, coagulation defects, organ transplant, liver disease, or pregnancy prior to receiving COVID-19 vaccine. A self-controlled case series analysis was used to estimate the incidence rate ratio (IRR) during the risk window (1-30 days after each dose) by fitting a conditional Poisson regression model. The control window was defined as the period of 1-120 days following the first vaccine dose, excluding the period that corresponds to the risk window. Subgroup analyses were conducted by age groups and vaccine products given prior to diagnosis.
Results: Among a total of 15,388,810 women who received the COVID-19 vaccine, 109,970 patients with AUB were identified with a mean age of 37.7 years (SD: 11.6 years). The risk of AUB within 30 days following COVID-19 vaccination was significantly higher compared to the risk within the control window (IRR = 1.42; 95% confidence interval: 1.40-1.44). The study's findings were consistent across all subgroup analyses.
Conclusions: The study demonstrates an increased risk of AUB following COVID-19 vaccination, regardless of the type of vaccine used. Further studies are needed to examine the severity and persistence of AUB following COVID-19 vaccination.
