Association between menstrual cycle pattern regularity and changes in menstrual bleeding following COVID-19 vaccination: secondary analysis of an observational study

COVID-19 vaccination is associated with small, temporary increases in menstrual cycle length and bleeding volume among individuals with regular cycles prior to vaccination. 1–3 However, post-vaccination menstrual disturbances among individuals with irregular cycles, who make up approximately one quarter of the menstruating population,4 have only been examined using cross-sectional retrospective reporting. This study used prospectively collected data to determine whether post-COVID-19 vaccination changes in menstrual bleeding volume and menses length differ by pre-vaccination cycle regularity patterns.