COVID Vaccines and Women's Health

COVID-19 vaccine tied to small, temporary increase in menstrual cycle length

(RxWiki News) Since COVID-19 vaccines became available, myths and misunderstandings have spread. But new research is starting to bust some of those myths with real data.

In the latest instance of this kind of research, a National Institutes of Health (NIH) study found that getting the COVID-19 vaccine was linked with a temporary increase in the length of women's menstrual cycles.

The increase of around one day on average was well within the normal range of variation, the study authors noted. And it wasn't specifically an extra day of bleeding — the length of the entire cycle appeared to increase.

Persistent rumors and myths surrounding women's health and fertility have plagued efforts to vaccinate the public. But this research provides actual facts that women can consider and prepare for as they get vaccinated and boosted.

“It is reassuring that the study found only a small, temporary menstrual change in women,” said Dr. Diana W. Bianchi, director of the NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, in a press release. “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.”

To conduct this research, the study authors analyzed data from a fertility tracking app. They looked at three menstrual cycles before vaccination and three cycles after vaccination in nearly 4,000 anonymous women who used the app.

The first vaccine dose was linked to an increase of 0.71 days in the menstrual cycle on average, these researchers found. The second dose was tied to a slightly longer increase at 0.91 days. The increases appeared to decrease in later cycles, suggesting that the increases were temporary.

Unvaccinated women in the study did not show a significant change in the length of their menstrual cycles.

According to the NIH, a variation of up to eight days in the length of a menstrual cycle can be considered normal.

If you have questions about the COVID-19 vaccines, reach out to your health care provider.

This study was published in the journal Obstetrics & Gynecology.

The NIH funded this research. Information on potential conflicts of interest was not available at the time of publication.

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Review Date: 
January 26, 2022