Association Between Menstrual Cycle Length and Coronavirus Disease 2019 (COVID-19) Vaccination.

To assess whether vaccination against coronavirus disease 2019 is associated with changes in cycle or menstrual length in vaccinated individuals compared to unvaccinated cohorts. We used the Natural Cycles application to analyze the positively recorded menstrual cycle data. US citizens aged 18-45 years, 3 consecutive cycles before the first vaccination (cycles 4-6), or a normal cycle length of 6 cycles (24-38 days) if not vaccinated there is. Period Included period. Averages within individual variations in cycle and menstrual length were calculated (3 cycles before vaccination vs. the first and second dosing cycles of the vaccinated cohort, and the first 3 cycles vs. the non-vaccinated cohort. Cycles 4 and 5). A mixed-effects model was used to estimate adjusted differences in cycle and menstrual length changes between vaccinated and non-vaccinated cohorts. We included 3,959 subjects (2,403 vaccinated; 1,556 unvaccinated). The majority of the vaccinated cohorts received the PfizerBioNTech vaccine (55%) (Moderna 35%, Johnson & Johnson / Janssen 7%). Overall, the COVID19 vaccine was associated with a change in cycle length of less than 1 day in both vaccination cycles compared to the pre-vaccination cycle (initial dose increased by 0.71 days, 98.75% CI 0.47-0.94). Second dose 0.91, 98.75% CI 0.63-1.19); Unvaccinated subjects showed no significant changes compared to the three baseline cycles (cycle 4 0.07, 98.75% CI -0.22). ~ 0.35; Cycle 5 0.12, 98.75% CI -0.15 ~ 0, 39). In the fitted model, the difference in cycle length change between the vaccinated and non-vaccinated cohorts was less than 1 day at both doses (difference in change: first dose 0.64 days, 98.75% CI 0.27-1.01; Second dose 0.79 days, 98.75% CI). 0.40-1.18). Changes in menstrual length were not associated with vaccination. The menstrual cycle is a clear sign of health and fertility. The characteristics of menstruation are not static and vary from month to month throughout a person's life. The International Federation of Gynecology and Obstetrics classifies cycle length fluctuations of less than 8 days as normal fluctuations. Normal menstruators can also experience sporadic or stress-related ovulatory disorders, which can lead to cycle failures or temporary changes in cycle length. This normal variation may be of concern, especially in connection with new exposures such as COVID19 vaccination.