During the pandemic, many women experienced high levels of stress as they took on a disproportionate share of child care and housework and dropped out of the labor force in large numbers.

Now, a new study suggests that all of this extra stress may have changed women’s menstrual cycles in a variety of ways. Some women who reported high levels of stress also reported early or delayed periods. Others had heavier menstrual flow or increased spotting between cycles. Some women said that during pandemic stress, their periods lasted more days than usual, while others said their periods got shorter.

Martina Anto-Ocrah, an assistant professor at the University of Pittsburgh School of Medicine, who led the study, called the results “alarming,” because of the effects an irregular cycle can have on fertility and mental health.

“This really extends beyond menstruation, it’s about women’s well-being,” she said.

The study, published in Obstetrics & Gynecology, relied on self-reported data from 354 women between the ages of 18 and 45. Women were asked in early May 2021 to answer questions about their pandemic-related stress and report any menstrual cycle changes that occurred between March 2020 and May 2021.

Over half of the women surveyed reported changes in their menstrual cycle length, period duration, menstrual flow, or spotting, and 12 percent of women reported a change in all four measures. The researchers found a significant association between high levels of pandemic-related stress and changes in the menstrual cycle.

Younger women and women with previously diagnosed mental health conditions were more vulnerable to feeling high stress and experiencing menstrual cycle changes. The study authors noted the data were collected from a racially diverse and geographically representative sample. The women were not on birth control, menopausal or postmenopausal before the pandemic. The study did not include trans or non-binary people who also have periods.

The research is part of a growing body of evidence suggesting that women’s periods changed during the pandemic.

“Women are constantly being told, ‘This is in your head,’ ” said Anto-Ocrah. “Until we get some data to show that what is in women’s heads is actually the truth, the medical society kind of turns us away and doesn’t believe it.”

Stress can affect a woman’s menstrual cycle in a number of ways. The stress hormone cortisol can affect the body’s production of estrogen and progesterone, which are reproductive hormones that influence the menstrual cycle. Stress-related factors, such as poor nutrition, weight gain, weight loss and poor sleep, also can play a role.

Nicole C. Woitowich, a medical research assistant professor at Northwestern University, found a similar association between period changes and pandemic stress in 2020 after conducting an online survey of 210 women. Because it wasn’t a representative sample, the findings aren’t conclusive. But Woitowich said both studies, conducted a year apart, suggest that the pandemic affected women’s stress levels and menstrual cycles over a long period of time.

“Women have really borne the brunt of the pandemic, from multiple facets,” Woitowich said. “From being the primary care giver, from dealing with remote learning, and oftentimes working while navigating that as well.”

Linda Fan, assistant professor of obstetrics and gynecology at the Yale School of Medicine, said she has seen an uptick of patients coming in to discuss irregular menstrual cycles. In general, one or two abnormal cycles isn’t something to worry about, but she encourages patients to talk to their doctors and to continue tracking their periods to be sure no concerning patterns emerge.

In addition to stress, changes in one’s menstrual cycle could also signal thyroid disease, hormonal changes, cancer, pregnancy or an infection, she said.

“It can be very alarming,” Fan said. “And I think that doctors may tend to underplay that.”

Because of pandemic restrictions, Marcela Wakeham, 46, of Lancing, England, wasn’t able to teach yoga and Pilates and took a job as a care worker. Her husband’s business closed at the same time.

She believes all the stress she experienced during that time may have triggered early menopausal symptoms, including shorter menstrual cycles as well as “violent” hot flashes and insomnia. But her doctor told her she was “too young” to be entering menopause and declined to prescribe the hormone treatment she wanted.

“I didn’t have a spare minute for myself,” Wakeham said. “My levels of stress were up to the roof.”

A prolonged irregular menstrual cycle sometimes can be a sign of more worrying changes in the body, said Amy Wagner, a professor at the University of Pittsburgh. If someone is in a chronically stressful situation, higher levels of cortisol over time can not only affect periods, but also can increase the risk of inflammation, autoimmune diseases, heart disease, high blood pressure or other chronic diseases, she said.

Caroline Fan, 41, of St. Louis said she felt “on edge” constantly during the pandemic because she worried that her husband, an infectious-disease doctor, would get covid. She was also helping to coordinate outreach programs to Asian American communities and was anxious about anti-Asian violence.

During this stressful time, she noticed her periods became heavier, her cycles got shorter and she had more painful cramping. She also missed one period entirely. Fan said she also lost weight and started having difficulty sleeping. “I was so anxious because I was running around trying to do all these things,” she said.

The length of her cycle has now returned to normal, but Fan said she still has more painful cramping that forces her to take time off work.

A recent report in the International journal of Epidemiology noted that questions about menstruation haven’t been included in most large-scale covid-19 studies. Gemma Sharp, an associate professor at the University of Exeter and the study’s lead author, said more research is needed to inform women if these stress-related changes in their cycle will have any lasting effects.

“From what we know about how the menstrual cycle is regulated, we think these changes are likely to be short-term and unrelated to long-term health and fertility, but it is absolutely crucial that scientists can produce evidence on this to give women the reassurance they deserve,” she said.