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Yes, the COVID vaccine could impact a woman's menstrual cycle, but experts say impact is minimal, temporary and shouldn't cause worry

Reports from women claiming the vaccine altered their menstrual cycle prompted the new research.

ATLANTA — Since the introduction of the COVID-19 vaccine, claims and questions have popped up from women wondering whether the vaccine altered their menstrual cycle and what that could mean for their heath.

Such anecdotes prompted a closer look from researchers. 

"It's a question I think we've all heard from people, friends, sisters, relatives," Dr. Sujuatha Reddy told 11Alive's Verify team. "I've heard it from patients."


Can getting the COVID-19 vaccine cause changes in a woman's menstrual cycle?


  • A new study published in the journal Obstetrics and Gynecology 
  • 11Alive Medical Correspondent Dr. Sujatha Reddy 


This is true.

Yes, new research shows the Covid-19 vaccine can alter a woman's menstrual cycle, but researchers emphasize the impact was minimal, temporary and should not cause worry. 


The study, which was published in the journal Obstetrics & Gynecology and funded by the National Institutes of Health, was conducted after some women reported irregular or missing menstrual periods or other menstrual changes after getting the COVID-19 vaccines.

Using anonymous data from a fertility tracking app, researchers found women who got one dose of a COVID-19 vaccine had an average menstrual cycle length of about one day longer than usual, compared to unvaccinated women. 

A smaller group who got two vaccine doses within the same cycle had an average cycle length of about two days longer, but the study also notes menstrual cycles typically vary a little each month, and such changes were in normal range.

The study included nearly 4,000 individuals, 2,403 of which were vaccinated and 1,556 were unvaccinated. The majority received the mRNA COVID-19 vaccines from Pfizer or Moderna.

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

Researchers note that while there was an increase in average cycle length for some, there was no reported change in the number of days of bleeding, according to the statement. 

Researchers concluded that the findings, however, verify it's true the COVID-19 vaccine can impact a woman's menstrual cycle. But experts say such changes are not clinically significant and should not cause worry.

"We've seen this as gynecologists over women's lifetimes for a variety of reasons," Dr. Reddy said. "We'll see it for physical, emotional stress. We'll see it with travel. So you know, anything that can affect your body really can affect your period."

"The change was temporary for one or two periods really, and only for a few days," Dr. Reddy said. "It's just not that big of a deal luckily."

Dr. Reddy also emphasized that there is no relationship between the vaccine and infertility. She adds that any temporary changes in a woman's menstrual cycle will not impact fertility in the long run.  

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