STUDY: Covid-19 Vaccines Briefly Impact Menstrual Cycles

New research points to slight changes in a person’s menstrual cycle after the COVID-19 vaccine

Did you notice changes in your period after receiving a COVID-19 vaccine? New research proves you may not be imagining it. A recent study in the journal Obstetrics & Gynecology points to the shot causing a slight change in a person’s menstrual cycle.

The new research shows that an increase in cycle length — less than a day — was found in study participants.

“(This research) is both reassuring and validating and provides us a counseling tool. It’s reassuring because we see that at a population level (change) is small,” Dr. Alison Edelman, an author on the paper and professor of obstetrics and gynecology at Oregon Health and Science University School of Medicine, tells TODAY. “That may mean something different to each individual who menstruates.”

It’s important to note that the study discovered a slight increase in cycle length among participants but not a longer bleeding period. For example, if your cycle is typically 30 days, the study suggests it could lengthen to 31, but if you usually bleed for four days, you would still bleed for the same length of time. The study found that the effects were temporary, with cycle lengths returning to normal within a month or two.

The length was slightly longer in people who received both vaccines within the same cycle — two days instead of one day extra added to their average cycle length. Dr. Hugh Taylor, the chair of the department of obstetrics, gynecology and reproductive sciences at Yale School of Medicine, tells The New York Times, “It validates that there is something real here,” with the doctor noting that he’s heard about menstrual irregularities from his patients.

“We know that menstruation can be impacted by a variety of factors, including stress, lifestyle changes or a range of underlying conditions,” Dr. Christopher M. Zahn, vice president for practice activities at the American College of Obstetricians and Gynecologists said in a statement obtained by TODAY. “The new paper published in Obstetrics & Gynecology provides important new evidence underscoring that any impact of the COVID vaccines on menstruation is both minimal and temporary.”

Zahn’s statement continues: “We continue to stress that the COVID vaccines have absolutely no impact on fertility. People should continue to feel confident in the decision to be vaccinated and, when eligible, to receive a booster, and we encourage everyone aged five and above to get vaccinated.”

Dr. Taylor was careful to point out that this new research shouldn’t stop people from getting the shot. “I want to make sure we dissuade people from those untrue myths out there about fertility effects,” he said. “A cycle or two where periods are thrown off may be annoying, but it’s not going to be harmful in a medical way.”