A study released Thursday suggests that the COVID-19 vaccine is linked to an average of less than a one-day change in menstrual cycles, which researchers say is no cause for alarm.
On average, menstrual cycles increased by 0.71 days after the first dose of the COVID-19 vaccine, and for those who received a second dose during the study, 0.91 days. When compared to a cohort of unvaccinated participants, there was not a significant increase in those who experienced a cycle change of more than eight days (which is considered clinically significant).
“It is reassuring that the study found only a small, temporary menstrual change in women,” said Diana W. Bianchi, M.D., director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, in a press release. “These results provide, for the first time, an opportunity to counsel women about what to expect from COVID-19 vaccination so they can plan accordingly.”
Dr. Alison Edelman, an obstetricia/gynecologist and professor at the Oregon Health & Science University, told CNN that while this finding is reassuring, many may find any change in their menstrual cycle concerning. This study can help them know what to expect.
“People have different relationships with their menstrual cycle,” she said. “For some people, maybe they’re planning pregnancy or trying to avoid a pregnancy. Even one day of change — and that’s a mean — can feel uncomfortable.”
On average, a menstrual cycle is approximately 25 to 30 days in length, however, many experience cycles outside of this range. Variations of up to eight days between cycles is considered normal by the International Federation of Gynecology and Obstetrics.
The study followed 3,595 participants; 2,403 who had been vaccinated tracked three menstrual cycles before their first vaccine dose, and then three cycles post vaccination. Of the vaccinated participants, 80 per cent had received a second dose of the vaccine by the last cycle tracked in this study.
Data was compared with that provided by 1,556 non-vaccinated individuals, who tracked six consecutive cycles. Individuals who had cycles outside of 24 to 38 day range were not included in the study.
The majority of vaccinated participants received the Pfizer-BioNTech vaccine (55 per cent), 35 per cent received Moderna and seven per cent received the one-step Johnson & Johnson/Janssen vaccine.
More research is needed to determine if the COVID-19 vaccination impacted other symptoms associated with menstruation, including flow, pain, and mood changes.
The U.S. National Institute of Health announced last summer that it had earmarked $1.7 million for research into potential links of the COVID-19 vaccination and changes in menstrual cycles.
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