Times points out, the set of women using the Natural Cycles app isn’t nationally representative—these users tend to be white, educated, thinner than the average American woman, and are not using hormonal contraception, making it difficult to draw generalizable conclusions.
Alison Edelman, M.D., a professor of obstetrics and gynecology at Oregon Health & Science University and the lead author of the study, also noted that there’s lots of room for individual variation in the data.
For example, a large factor influencing the findings was a group of 380 women who experienced a two-day delay in the start of their period, she told the Times.
A smaller group of vaccinated women—about 5%, per —experienced cycles eight days longer than normal. (However it’s also worth noting that this number was the same among unvaccinated women in the study.) “Though the cycle length was less than one day different at the population level, for an individual, depending on their perspective and what they’re relying on menses for, that could be a big deal,” she said. “You might be , you might be worrying about a pregnancy, you might be wearing white pants.”The study also doesn’t address reports from post-menopausal women (who aren’t likely to be using the app).