COVID-19 Vaccines Can Change The Length Of A Person's Menstrual Cycle, A New Study Says

Findings from a peer-reviewed study suggest that a person's menstrual cycle can temporarily change after getting a COVID-19 vaccine when compared to someone who is unvaccinated.

The vaccine "is associated with a small change in cycle length but not menses length," concluded the study, which appears in the journal Obstetrics & Gynecology.

Researchers saw a one-day increase in the length of time between bleeding, although they did not see an increase in the number of bleeding days.

The authors pointed out that menstrual cycles are never consistent and tend to change every month.

“We included U.S. residents aged 18–45 years with normal cycle lengths (24–38 days) for three consecutive cycles before the first vaccine dose followed by vaccine-dose cycles (cycles 4–6) or, if unvaccinated, six cycles over a similar time period,” said the study.

"It is reassuring that the study found only a small, temporary menstrual change in women," Diana W. Bianchi, director of the National Institute of Health, said in a news release. The NIH funded the study.

"These results provide, for the first time, an opportunity to counsel women about what to expect from COVID-19 vaccination so they can plan accordingly,” Bianchi said.

Dr. Bianchi also added that there hadn’t been adequate research done on how COVID-19 vaccines or other vaccines for diseases can affect the menstrual cycle, so this study is a big step forward in women’s health research.

The study had 3,959 participants, of which 2,403 were vaccinated and 1,556 were unvaccinated.

Most of the vaccinated individuals had received either the Pfizer vaccine or Moderna vaccine. Those who received one dose saw an increase one their mensural cycle by 0.71 days, while those who were double vaccinated had their cycle increase by 0.91 days.

However, the study also found that the change was temporary and tended to go back to normal in subsequent menstrual cycles.

The press release also acknowledges that there is still a lot to research regarding the effect of the vaccine on other aspects of a woman’s menses, such as irregularities in bleeding, accelerated symptoms and missed periods.