To evaluate how stress related to the coronavirus disease 2019 (COVID-19) pandemic has affected women's menstrual cycles. We hypothesized that women with high levels of COVID-19-related stress would have more menstrual changes compared with those with lower levels of stress.METHODS: Using a cross-sectional study design, we recruited a representative sample of U.S. adult women of reproductive age (18-45 years) using nonhormonal birth control to participate in an online REDCap (Research Electronic Data Capture, Vanderbilt University) survey. COVID-19-related stress was assessed with the PSS-10-C (COVID-19 Pandemic-related Perceived Stress Scale) and dichotomized as low stress (scores lower than 25) and high stress (scores 25 or higher). Self-reported menstrual outcomes were identified as changes in cycle length, duration, or flow and increased frequency of spotting between cycles. We used x 2 and Fisher exact tests to compare differences in outcome between the two stress groups and logistic regression models for effect estimates.