Menstrual Changes Confirmed Following COVID-19 Vaccination

A recent analysis of reports from more than 35,000 women offers a comprehensive assessment of menstrual changes experienced by pre- and post-menopausal females in the first two weeks after receiving the COVID-19 vaccine.

Published in the journal Science Advances on July 15, 2022, the study found that 42% of women with regular menstrual cycles bled more heavily than usual, while 44% reported no change after vaccination.

Among respondents, 66% of post-menopausal women reported breakthrough bleeding.

These researchers found that increased/breakthrough bleeding was significantly associated with age, systemic vaccine side effects (fever and/or fatigue), history of pregnancy or birth, and ethnicity.

Generally, changes to menstrual bleeding are not uncommon or dangerous, yet attention to these experiences is necessary to build trust in medicine, stated these researchers.

“Menstruating and formerly menstruating women began sharing that they experienced unexpected bleeding after being administered a COVID-19 vaccine in early 2021,” wrote the scientists who led the study.

Because vaccine trials typically do not ask about menstrual cycles or bleeding, this side effect was largely ignored or dismissed.

“We focused our analysis on those who regularly menstruate and those who do not currently menstruate but have in the past,” commented Kathryn Clancy, a professor of anthropology at the University of Illinois Urbana-Champaign, in a related press release.

“The latter group included post-menopausal individuals and those on hormonal therapies that suppress menstruation, for whom bleeding is especially surprising.”

Because the study relied on self-reported experiences logged more than 14 days after vaccination, it cannot establish causality or be seen as predictive of people in the general population.

But it can point to potential associations between a person’s reproductive history, hormonal status, demographics, and changes in menstruation following COVID-19 vaccination.

For example, the analysis revealed that respondents who had experienced a pregnancy were most likely to report heavier bleeding after vaccination, with a slight increase among those who had not given birth.

Most non-menstruating premenopausal respondents on hormonal treatment experienced breakthrough bleeding after receiving the vaccine.

More than 70% of respondents using long-acting reversible contraception and 38.5% of those undergoing gender-affirming hormone treatments reported this side effect.

“Unexpected breakthrough bleeding is one of the early signs of some cancers in post-menopausal people and in those who use gender-affirming hormones, so experiencing it can make people worry and require expensive and invasive cancer-screening procedures,” said Katharine Lee, an anthropology professor at Tulane University.

“Menstruation is a normal process that responds to all kinds of immune and energetic stressors. People notice changes to their bleeding patterns, yet we don’t tend to talk about it publicly.”

The Beckman Institute, the CSBS, and the Interdisciplinary Health Sciences Institute at Illinois supported this research, as did the National Institutes of Health, the Foundation for Barnes-Jewish Hospital, and the Siteman Cancer Center in St. Louis, MO.

Note: This study and press release were manually curated for mobile readers.