(WKBN) – A new study funded by the National Institutes of Health shows that the COVID-19 vaccine may temporarily lengthen menstrual cycles.
Women receiving one dose of a COVID-19 vaccine during a single menstrual cycle had an increase in cycle length of nearly one day, compared to unvaccinated women, according to NIH.
Most study participants received the Pfizer and Moderna vaccines. On average, the first vaccination dose was associated with a .71-day cycle increase in cycle length and the second dose with a .91-day increase.
The increase in cycle length—a longer time between bleeding—was not associated with any change in the number of days of menses (days of bleeding). The study appears in Obstetrics & Gynecology.
Researches said menstrual cycles typically vary from month to month, and the increase they saw was within the range of what is considered a normal variation, adding that additional research is needed to determine if the vaccine impacts other characteristics of menstruation like pain, mood change, heaviness of flow, etc.
“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 (NICHD). “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.”
Bianchi said that little research has been done on how vaccines for COVID-19 or for other diseases could influence the menstrual cycle.
NIH funded the study, which was part of a $1.6 million award to NIH and four other institutions to explore links between COVID-19 vaccination and menstrual changes.