Women’s period may be late after coronavirus vaccination, study finds

Shortly after the coronavirus vaccines rolled out about a year ago, women began to report erratic menstrual cycles after receiving the injections.

Some said their period was late. Others have reported more bleeding than usual or painful bleeding. Some postmenopausal women who haven’t had a period for years have even reported having their period again.

A study published Thursday found that women’s menstrual cycles have done indeed change following the vaccination against the coronavirus. The authors reported that women who were vaccinated had slightly longer menstrual cycles after receiving the vaccine than those who had not been vaccinated.

Their periods themselves, which came almost a day later on average, however, were not prolonged and the effect was transient, with cycle lengths returning to normal within a month or two. For example, a person with a 28-day menstrual cycle that begins with seven days of bleeding would always start with a seven-day period, but the cycle would last for 29 days. The cycle ends when the next period begins and would return to 28 days in a month or two.

The delay was more pronounced in women who received both doses of the vaccine in the same menstrual cycle. These women got their period two days later than usual, the researchers found.

The study, published in the journal Obstetrics & Gynecology, is one of the first to substantiate anecdotal reports from women that their menstrual cycles were interrupted after vaccination, said Dr Hugh Taylor, director of the obstetrics department, of Gynecology and Reproductive Sciences at Yale. Medicine School.

“This confirms that there is something real here,” said Dr Taylor, who has heard of irregular cycles from his own patients.

At the same time, he added, the changes seen in the study were not significant and appeared to be transient.

“I want to make sure that we dissuade people from these false myths about the effects on fertility,” Dr. Taylor said. “A cycle or two where your period is interrupted can be annoying, but it won’t be medically harmful.”

He had a different message for postmenopausal women who experience vaginal bleeding or vaginal bleeding, whether after vaccination or not, warning that they may have a serious health problem and should be evaluated by a doctor.

A serious drawback of the study, which focused on US residents, is that the sample is not nationally representative and cannot be generalized to the entire population.

The data was provided by a company called Natural Cycles which is creating an app to track fertility. Its users are more likely to be white and have a college education than the general US population; they are also thinner than the average American woman – weight can affect menstruation – and do not use hormonal contraception.

For women of childbearing age, the results should be reassuring, said Dr Diana Bianchi, director of the National Eunice Kennedy Shriver Institute of Child Health and Human Development. (The National Institutes of Health’s Women’s Health Research Office and NICHD helped fund the study, as well as related research projects at Boston University, Harvard Medical School, Johns Hopkins, and at Michigan State University.)

“Their providers may say, ‘If you have an extra day, that’s okay, it’s not something to worry about,’” Dr Bianchi said.

The study was conducted by researchers at Oregon Health & Science University and Warren Alpert Medical School at Brown University, working with researchers from Natural Cycles, whose app is used by millions of women. in the world.

The anonymized data of users who consented to have their information included in the research provided a wealth of evidence on how women’s cycles changed during the pandemic.

Researchers examined the records of nearly 4,000 women who had meticulously tracked their periods in real time, including about 2,400 who were vaccinated against the coronavirus and about 1,550 who were not. All were U.S. residents between the ages of 18 and 45 who had recorded their period for at least six months.

For those who were vaccinated, the researchers looked at the three cycles before and after the vaccine to look for changes, comparing them to a similar duration of six months in women who did not receive a vaccine.

Overall, vaccination was associated with less than a full day of change in cycle length, on average, after the two doses of vaccine, compared to pre-vaccine cycles. The unvaccinated group saw no significant changes over the six months.

Future studies using the database will look at other aspects of menstruation, such as whether periods were heavier or more painful after vaccination.

The new study’s results may not apply equally to all women. Indeed, much of the change in cycle length was brought about by a small group of 380 vaccinated women who experienced a change of at least two days in their cycle, said Dr. Alison Edelman, professor of obstetrics. and gynecology at Oregon Health & Science University. and the main author of the article.

Some vaccinated women had cycles that were eight days longer than usual, which is considered clinically significant, Dr Edelman said.

“Although cycle length is different by less than a day at the population level, for an individual, depending on their perspective and why they are relying on their period, it could be a big deal. “she said. “You might be pregnant, you might be worried about pregnancy, you might be wearing white pants.”

It is not known why the menstrual cycle may be affected by vaccination, but most women with regular periods sometimes experience an unusual cycle or missed periods. Hormones secreted by the hypothalamus, pituitary, and ovaries regulate the monthly cycle, and they can be affected by environmental factors, stressors, and life changes.

(The changes seen in the study were not caused by conditions related to the pandemic, the authors said, because the women in the unvaccinated group were also living in the pandemic.)

It is not known whether other vaccines affect menstruation – clinical trials of vaccines and therapeutics generally do not track menstrual data points, unless investigators specifically test therapeutics like contraceptives or fertility enhancers, or that they want to rule out pregnancy.

“We hope this experience will encourage vaccine makers and clinical trials of therapies to ask questions about the menstrual cycle, in the same way you would include other vital signs,” said Dr Bianchi.

Information is important, as is knowing that one may have a headache or develop a fever after vaccination, said Dr Edelman.

“People who have their period spend a week a month, sometimes longer, dealing with their period,” said Dr. Edelman. “If you add the time over 40 years, that’s almost ten years of menstruation.”


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