It’s completely normal for menstrual cycles to vary slightly from month to month, but if you’ve noticed unusual changes right around the time you had COVID-19 or the vaccination that helps prevent it, it’s not all in your head. You’re part of a scientifically recognized crowd.
Consider the results of an international study of more than 6,000 people, published August 2023 in the journal Obstetrics and Gynecology. This research is simply the latest showing that people with COVID-19 may experience small, temporary changes in menstrual cycle length.
Among unvaccinated subjects who reported having COVID-19, the scientists calculated a 1.45-day increase in menstrual cycle length compared with previous cycle length average.
As for the impact of COVID-19 vaccination, another study published June 2023 in the journal Vaccine confirms previous research linking immunization with a temporary average increase in menstrual cycle length — of about a day, the scientists found.
The study, which involved 1,137 participants, found no association between COVID-19 vaccination and menstrual cycle regularity, bleed length, period heaviness, or menstrual pain.
The COVID-19 Vaccine Can Lead to Vaginal Bleeding in Women Who Don’t Menstruate
A study published September 2023 in Science Advances looked at the effect of the Moderna and Pfizer COVID-19 vaccines on nonmenstruating women, including those who are postmenopausal, perimenopausal, or premenopausal (most of whom were opting for birth control with a hormonal IUD, which halts menstruation).
“Our findings indicate that the COVID-19 vaccines, or the host response to them, can lead to vaginal bleeding in a wide range of women,” the study authors concluded.
Among the 7,725 women in the study, a small percentage experienced unexpected vaginal bleeding within eight to nine months of vaccination: about 3 percent of postmenopausal women (which is double or triple the typical rate), 14 percent of perimenopausal women, and 13 percent of premenopausal women.
The COVID-19 Vaccine May Cause Bleeding in People Using Hormones That Suppress Menstruation
An online survey by researchers at Washington University in St. Louis, presented in April 2022, was the first to specifically assess breakthrough bleeding caused by the COVID-19 vaccine in people who take testosterone or other hormones that suppress menstruation as part of gender-affirming healthcare.
The survey included individuals with a range of gender identities, such as transgender, nonbinary, or gender-fluid.
The researchers discovered that, of 552 respondents who said they used testosterone or other gender-affirming hormones and did not usually menstruate, one-third reported breakthrough bleeding after they received a COVID-19 vaccine, 9 percent reported chest or breast soreness, and 46 percent reported having other symptoms they would usually associate with a period, such as cramping and bloating.
The study did not report the percentage of respondents who experienced breakthrough bleeding before vaccination, and it’s important to note that menstruation is not always reliably suppressed with these therapies.
A coauthor of the study, Katharine Lee, PhD, a postdoctoral research scholar in the division of public health sciences at Washington University in St. Louis, suspects the culprit for these changes is the immune and inflammatory response triggered by the vaccine: “There is a huge mobilization of your immune system. And I think it could just be a little bit of cellular cross-talk that is disrupting this process.”
Stress Related to the Pandemic Can Also Mess Up Your Period
Sometimes stress alone can throw your period out of whack, and if you’re someone who’s usually very regular, even slight differences are noticeable. In case you need any convincing, there’s no question that the COVID-19 pandemic and other distressing developments in recent history qualify as a major form of stress.
The pandemic has brought the kinds of intense personal challenges that can really disrupt lives, whether that’s losing a loved one, managing remote work for yourself, or getting divorced.
So it’s not exactly surprising that some people who menstruate have been experiencing disruptions — from skipped periods to longer cycles to changes in bleeding patterns.
“What we can say about COVID-19 and its effects on the menstrual cycle is comparable to what we can say about other viral infections and prolonged periods of stress — menstrual disruptions are likely to occur,” says Taraneh Shirazian, MD, the director of global women’s health and an assistant professor of obstetrics and gynecology at NYU Langone Health in New York City. “If you get COVID-19, it’s a stress on the body and a major stress on the hypothalamic pituitary adrenal (HPA) axis,” which is the body’s central stress response system.
During times of stress, the HPA axis stimulates the release of the stress hormone cortisol to help the body prepare to fight or flee from a threat. With ongoing stress, “increased cortisol levels can affect a woman’s menstrual cycles,” Dr. Shirazian says. In addition, with prolonged periods of stress, the stress response system can burn out, and the HPA axis can be suppressed, which drives down the pituitary production of follicle stimulating and luteinizing hormones (FSH and LH), which then drive down ovarian production of estrogen and progesterone.
With complete suppression of the HPA axis, a woman may experience amenorrhea, the absence of periods. With partial suppression, a woman could have spotty periods or periods of bleeding every few weeks. “There isn’t one clear pattern we can expect — women respond differently to suppression of the HPA axis,” Shirazian says.
A 1-2 Punch to Menstrual Periods
“The thing that’s important to emphasize is: Any illness can cause menstrual irregularities,” says Lauren Streicher, MD, a clinical professor of obstetrics and gynecology at Northwestern University in Chicago. “When you look at the combination of a serious infection [such as COVID-19] and the stress of the pandemic, it’s to be expected. How much of this is due to this specific infection versus any chronic stress or infection isn’t known and hasn’t been studied.”
It’s important to remember that “biologically, women menstruate for one reason and one reason only — to get pregnant,” Dr. Streicher adds. The dysregulation of the menstrual cycle that may be induced by COVID-19 infection may be a biological and evolutionary protective mechanism, both for the woman and for her potential offspring.
As far as the stress of the pandemic goes, it’s occurring on two fronts. Besides the fact that stress itself increases cortisol levels, which can affect menstruation, the disruptions that have occurred in people’s lifestyles and routines during the pandemic can affect a woman’s menstrual cycle. And if women have become more sedentary or gained weight during the pandemic, Shirazian notes, these changes can affect their periods, perhaps leading to missed menstrual periods, longer spans between periods, or longer bleeding time.
Indeed, “any stressful situation can alter hormone levels and cause someone not to menstruate regularly,” Streicher says. “Mostly it’s because ovulation is not occurring.”
Taking Back the Monthly Menstrual Period
If you experience a change in your periods, the first step is to consider whether you could be pregnant. If you confirm that you’re not pregnant and “you miss a period for a month or two but you’re otherwise feeling fine, it’s not something to panic about,” Streicher says.
Additional reporting by Monroe Hammond and Stacey Colino.