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This fact brief was originally published as an experiment to test the concepts behind fact briefs.
Readers should be aware that while there is still a lot of useful information in fact briefs like this one, not all of them reflect Gigafact's current methods and standards for fact briefs. If you come across any that you feel are out of date, don't hesitate to contact us at support@gigafact.org.
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FACT BRIEF

Can the COVID-19 vaccine affect women’s menstrual cycles?

By Lisa Freedland
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YES

Analyzing data from nearly 4,000 women between the ages of 18 and 45, a study collecting data through a menstrual cycle tracking app found that women vaccinated with the COVID-19 vaccine experienced a slight, temporary increase in the time between their menstrual cycles. 

Researchers discovered that on average, women who received their first COVID-19 vaccine saw a temporary cycle length increase of 0.71 days, while women who received their second during the study saw a 0.91-day increase. Researchers noted, "The increase in cycle length for both the first and second vaccine cycles appears to be driven largely by the 358 individuals who received both vaccine doses within a single [menstrual] cycle."

Menses, or days of bleeding, did not increase in the vaccinated group relative to the unvaccinated group.

Scientists caution that menstrual cycle changes of less than eight days are normal and encourage women to continue receiving the COVID-19 vaccine.

This fact brief is responsive to conversations such as this one.
Sources
Lippincott Research Association Between Menstrual Cycle Length and Coronavirus D... : Obstetrics & Gynecology
National Institutes of Health COVID-19 vaccines linked to small increase in menstrual cycle length
Hackensack Meridian Health What You Should Know About COVID Vaccines & Menstrual Cycles
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Gigafact
Between 2020 and 2022, under close editorial supervision, Gigafact contracted a group of freelance writers and editors to test the concepts for fact briefs and provide inputs to our software development process. We call this effort Gigafact Foundry. Over the course of these two years, Gigafact Foundry writers published over 1500 fact briefs in response to claims they found online. Their important work forms the basis of Gigafact formats and editorial guidelines, and is available to the public on Gigafact.org. Readers should be aware that while there is still a lot of relevant information to be found, not all fact briefs produced by Gigafact Foundry reflect Gigafact's current methods and standards for fact briefs. If you come across any that you feel are out of date and need to be looked at with fresh eyes, don't hesitate to contact us at support@gigafact.org.
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About fact briefs published on Gigafact
Fact briefs are short, credibly sourced summaries that offer “yes/no” answers in response to claims found online. They rely on publicly available, often primary source data and documents. Fact briefs are created by contributors to Gigafact —a nonprofit project looking to expand participation in fact-checking and protect the democratic process. See all fact briefs here.