HealthDay News — COVID-19 vaccination is associated with a small and mainly transient change in menstrual cycle length, according to a study published online Sept. 28 in BMJ Medicine.
Alison Edelman, M.D., M.P.H., from the Oregon Health & Science University in Portland, and colleagues conducted a global cohort study of prospectively collected data for international users of the menstrual cycle tracking application, Natural Cycles. Data were included for 19,622 individuals aged 18 to 45 years with cycle lengths of 24 to 38 days and with data for at least three cycles before and one after vaccination (14,936 participants [vaccinated group]) and with at least four consecutive cycles (4,686 participants [unvaccinated group]).
The researchers found that compared with individuals who were not vaccinated, those who were vaccinated had a less than one-day adjusted increase in the length of their first and second vaccine cycles (0.71-day increase for first dose; 0.56-day increase for second dose). A larger adjusted difference was seen for those who received two doses in one cycle (3.70-day increase). For individuals who received one dose per cycle, cycle length was similar to before the vaccine at one cycle after vaccination; individuals who received two doses per cycle had a 0.85-day change compared with unvaccinated individuals. Vaccination did not affect menses length.
“Although we do find menstrual changes after COVID-19 vaccination, these changes are small compared with normal variation and resolve in the cycle after vaccination, except in people who received both doses in one menstrual cycle,” the authors write.
Several authors disclosed financial ties to the pharmaceutical and medical technology industries.