Can the COVID-19 vaccine affect menstruation?
Ask the doctors
Q. My daughter read that COVID-19 vaccination might affect a woman's menstrual cycle. Is there any truth to this?
A. A study published online Jan. 5, 2022, by Obstetrics and Gynecology suggests that on average, women experience a small (less than one day) increase in menstrual cycle length (counted in days from the start of one period to the start of the next) after COVID-19 vaccination, compared with pre-vaccination cycles. This variation is temporary and harmless, and there is no evidence that it affects a woman's health or fertility. It should also not dissuade women from getting the vaccine, which is effective and safe.
To examine menstrual cycle changes after vaccination, the study authors looked at data from a fertility tracking app called Natural Cycles. The study included self-reported menstrual cycle information from 2,403 vaccinated and 1,556 unvaccinated women, ages 18 to 45, who had normal cycle lengths (24 to 38 days) for three consecutive cycles. The vaccinated group included women who received the Pfizer, Moderna, and Johnson & Johnson vaccines. Researchers looked at menstrual cycle data for vaccinated women for six consecutive cycles, starting three cycles before vaccination. For the unvaccinated participants, researchers used information from six cycles over a similar time period.
On average, the vaccinated women saw an increase of .71 day in cycle length with the first dose of vaccine and an increase of .91 day with the second (if they received a two-shot vaccine). Women who got both doses of vaccine during one menstrual cycle saw a slightly larger increase (two days on average) in their cycle length, but this returned to baseline within two cycles. The unvaccinated women did not see a statistically significant change in cycle length. Importantly, vaccination made no difference in the number of days of bleeding. The researchers said that more study is needed to determine if vaccination affected any other aspects of menstruation, including symptoms or amount of menstrual flow.
About the Authors
Toni Golen, MD, Editor in Chief, Harvard Women's Health Watch; Editorial Advisory Board Member, 天博体育 Publishing; Contributor
Hope Ricciotti, MD, Editor at Large, Harvard Women's Health Watch
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