Many women have suspected it but finally there's confirmation that Covid-19 vaccines may cause some small changes to the length of their menstrual cycles.
A study funded by the United States National Institutes of Health (NIH) found the length of a woman's cycle was impacted by nearly one day on average after each dose of a vaccine, but it did not seem to impact the number of days of bleeding.
Dr Alison Edelman of Oregon Health & Science University, the lead author of the study published in Obstetrics & Gynecology, said menstrual cycles typically varied a small amount from month to month, and the increase they saw was well within the range of normal variability.
"It is reassuring that the study found only a small, temporary menstrual change in women," Dr Diana Bianchi, director of NIH's Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) added.
"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."