Aim: To assess whether coronavirus disease 2019 (COVID-19) vaccination is associated with changes in menstrual cycle or duration in vaccine recipients compared to an unvaccinated cohort. Methods: We analyzed menstrual cycle data with prospective follow-up using the “Natural Cycles” app. We included US residents aged 18 to 45 years with normal cycle length (24 to 38 days) for three consecutive cycles before the first vaccine dose followed by vaccine dose cycles (cycles 4 to 6) or, if unvaccinated, six cycles over a similar period. time frame. We calculated the mean intraindividual change in menstrual cycle and duration (three pre-vaccine cycles vs. first- and second-dose cycles in the vaccinated cohort, and the first three cycles vs. cycles four and five in the unvaccinated cohort). vaccinated). We used mixed-effects models to estimate the adjusted difference in the change in menstrual cycle and duration between the vaccinated and unvaccinated cohorts. Results: 3,959 people were included (2,403 vaccinated; 1,556 unvaccinated). The majority of the vaccinated cohort received the Pfizer-BioNTech vaccine (55%) (Moderna 35%, Johnson & Johnson/Janssen 7%). Overall, the COVID-19 vaccine was associated with less than 1 day change in cycle length for both vaccine dose cycles compared to pre-vaccine cycles (first dose 0.71 day increase, 98 .75% CI: 0.47-0.94; second dose 0.91, 98.75% CI 0.63-1.19); unvaccinated individuals did not see any significant change compared to three initial cycles (cycle four 0.07, 98.75% CI -0.22 to 0.35; cycle five 0.12, 98.75% CI : -0.15 to 0.39). In adjusted models, the difference in change in cycle length between the vaccinated and unvaccinated cohorts was less than 1 day for 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). The change in the duration of menstruation was not associated with vaccination. Conclusion: Vaccination against coronavirus disease 2019 (COVID-19) is associated with a small change in cycle length, but not in the duration of menstruation. |
Comments
Women who received a dose of the COVID-19 vaccine during a single menstrual cycle had an increase in cycle length of nearly a day, compared to unvaccinated women, according to a study funded by the National Institutes of Health.
The increase in cycle length, a longer time between bleeding, was not associated with any change in the number of days of menstruation (bleeding days).
The study appears in Obstetrics & Gynecology .
The authors, led by Alison Edelman, MD, MPH, of Oregon Health & Science University, Portland, noted that menstrual cycles generally vary a small amount from month to month, and the increase they saw was within the range of normal variability .
They added that additional research is needed to determine how the COVID-19 vaccine could potentially influence other menstrual characteristics, such as associated symptoms (pain, mood swings, etc.) and bleeding characteristics (including heaviness of flow).
“It is reassuring that the study found only a small temporary menstrual change in women,” said Diana W. Bianchi, MD, director of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). "These results provide, for the first time, the opportunity to advise women on what to expect from COVID-19 vaccination so they can plan accordingly."
Dr. Bianchi added that little research has previously been done on how vaccines for COVID-19 or vaccines for other diseases could potentially influence the menstrual cycle.
The NICHD and the NIH Office of Women’s Health Research funded the study, which was part of $1.67 million awarded to five institutions to explore possible links between COVID-19 vaccination and menstrual changes.
The study authors analyzed de-identified data from a fertility tracking app, Natural Cycles. Users enter data about their temperature and menstrual cycles and can consent to the use of their anonymous data for research.
For vaccinated people, data were from three consecutive cycles before vaccination and three more consecutive cycles, including the cycle or cycles in which vaccination occurred. For unvaccinated people, data was collected for six consecutive cycles. Of the 3,959 people in the study, 2,403 were vaccinated and 1,556 were not vaccinated.
Most vaccinated users received the Pfizer and Moderna vaccines . On average, the first dose of vaccination was associated with a .71-day increase in cycle length and the second dose with a .91-day increase in cycle length.
Therefore, users vaccinated for two cycles had an increase of less than one day in each of the vaccination cycles. There was no change in the number of days of menstrual bleeding for vaccinated people. The researchers did not see any significant change in cycle length for unvaccinated app users.
A subgroup of app users who received two doses of the vaccine in the same menstrual cycle (358 users) had a larger average increase in cycle length of two days. However, this change appears to decrease in subsequent cycles, indicating that the menstrual changes are likely temporary. The authors added that the International Federation of Gynecology and Obstetrics classifies a change in cycle length as normal if the change is less than eight days.
Reference
Edelman, A. et al. Association Between Menstrual Cycle Length and Coronavirus Disease 2019 (COVID-19) Vaccination: A US Cohort. Obstetrics & Gynecology . DOI:10.1097/AOG.0000000000004695 (2022)
