The largest study to date shows how COVID vaccines affect periods

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The largest study to date shows how COVID vaccines affect periods

Almost half of the participants in a recent study who were menstruating regularly at the time of the survey reported heavier bleeding during their period after receiving the COVID-19 vaccine. Others who don’t normally menstruate – including transgender men, people on long-acting contraceptives, and postmenopausal women – also had unusual bleeding.

The new study — the largest to date — expands research that has highlighted the temporary effects of COVID-19 vaccines on the menstrual cycle, but has so far mostly focused on menstruating cisgender women.

Although the vaccines have largely prevented deaths and serious illnesses with few reported side effects, many medical experts initially brushed aside concerns when women and people of opposite sexes began reporting irregular menstrual cycles after receiving the vaccines.

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To get a better picture of these post-vaccination experiences, researchers from the University of Illinois at Urbana-Champaign and Washington University School of Medicine in St. Louis conducted an online survey of thousands of people around the world in April 2021 distributed. After three months, the researchers collected and analyzed more than 39,000 responses from people between the ages of 18 and 80 about their menstrual cycles. All respondents to the survey were fully vaccinated—with vaccines from Pfizer-BioNTech, Moderna, Johnson & Johnson, or others approved outside of the United States. And to the best of our knowledge, the participants had not contracted COVID-19 prior to vaccination.

The study, published Friday in the journal Science Advances, shows that 42% of people with regular menstrual cycles had heavier bleeding after vaccination, while 44% reported no change and 14% reported lighter periods. In addition, 39% of those on sex-affirming hormone treatments, 71% of those on long-acting contraceptives, and 66% of postmenopausal women experienced breakthrough bleeding after one or both vaccinations.

“I think it’s important for people to know that this can happen so they don’t get scared, they don’t get shocked, they don’t get caught without supplies,” said Katharine Lee, a biological anthropologist at Washington University School of Medicine in Washington Washington St. Louis and first author of the study.

However, Lee warned that the study does not compare the results to a control group of people who were not vaccinated. And it’s possible that people who saw changes in their cycle after vaccination were more likely to take the survey. Nevertheless, the results are consistent with smaller studies that have reported menstrual changes after vaccination with more robust controls.

Importantly, the new study also found that some populations are more likely to experience menstrual changes, and the study may help them be more prepared, Lee said. For example, older women were more likely to have heavier menstrual periods. Respondents who used hormonal birth control, were pregnant in the past, or who had been diagnosed with a reproductive condition such as endometriosis, fibroids, or polycystic ovary syndrome were also more likely to have heavy bleeding during their period. People who identified as Hispanic or Latino also tended to report more bleeding. And people who experienced other side effects from the vaccines, such as fever or fatigue, also had a higher risk of experiencing irregular periods.

Postmenopausal women who were slightly younger, about an average age of about 60, were more likely to have had breakthrough bleeding after vaccination than older women. But the type of vaccine postmenopausal women received, whether they had other side effects like fever, or whether they had a past pregnancy didn’t seem to affect their bleeding.

Why are these changes occurring?

A certain amount of fluctuation in menstrual periods – the number of days you bleed, how heavy your flow is, and your cycle length – is normal.

“Our menstrual cycles are not perfect clocks,” said Dr. Alison Edelman, a professor of obstetrics and gynecology at Oregon Health & Science University who has also studied the effect of COVID-19 vaccines on menstruation.

Hormones secreted by the hypothalamus, pituitary gland and ovaries regulate the menstrual cycle and can be influenced by both internal and external factors. Stress and illness, weight loss or weight gain, calorie restriction and intense exercise can all alter typical menstrual patterns.

The endometrium, which lines the uterus and is shed during menstruation, has also been linked to the immune system. Because of the role it plays in remodeling uterine tissue and providing protection from pathogens, it’s possible that when vaccines activate the immune system, which they are supposed to do, they may also somehow trigger downstream effects in the endometrium and cause a disruption in your menstrual cycle, said Edelman. And some individuals may be more sensitive to immune or hormonal changes in their body.

In her research, Edelman found that some women’s periods came a day or two later than usual after they were vaccinated against the coronavirus. But the changes were temporary – menstruation tended to return to normal after a cycle or two.

What to do if you notice menstrual irregularities after the COVID vaccination?

If you notice new or unusual bleeding patterns, pay attention. The menstrual cycle can be thought of as another vital sign, just like your body temperature or blood pressure, that gives clues about your health, said Dr. Jennifer Kawwass, a reproductive endocrinologist at Emory University who was not involved with the study.

“A significant change in menstrual cycle interval or bleeding profile warrants further investigation to ensure that there is no underlying endocrine, hematologic, or anatomical cause,” Kawwass said. Breakthrough bleeding in people who are no longer menstruating, for example, can also be a warning sign of cervical, ovarian, uterine or vaginal cancer.

That said, minor fluctuations in your menstrual cycle shouldn’t be a cause for concern if you have regular periods, and don’t require you to change anything you normally would, Kawwass said.

Clinical trials and other studies have already established that the COVID-19 vaccines are safe, effective and unlikely to affect fertility in the long term.

Should you get vaccinated at a certain point in your cycle?

Experts agree that the havoc COVID-19 can wreak throughout the body, including possible after-effects, is far worse than any side effects caused by vaccination against the disease.

People who have previously developed a fever after an injection can schedule their next dose on a day when they don’t have to go to work, Edelman said. However, you should not let temporary menstrual changes prevent you from getting a full vaccination or booster. As cases rise again, delaying vaccination by two weeks or more can significantly increase your risk of catching COVID-19, she said.

Still, tracking your body’s response to the vaccine is important, and public health officials should acknowledge concerns about menstrual cycle fluctuations and warn people about the risk of catching COVID-19, bioethics expert Keisha Ray said from McGovern Medical School at UTHealth Houston.

The increased transparency regarding menstrual changes or other side effects of vaccinations could also have another benefit: reducing people’s hesitancy about vaccinations.

“We try to be honest. We’re trying to validate people’s lived experiences,” Lee said. In turn, she hopes the new research will help improve conversations about people’s health and lead to broader clinical trials in the future.

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