COVID-19-related stress has been linked to “silent” disruptions to ovulation in women without obvious changes to menstrual cycles, according to new research.

Nearly two-thirds of those studied experienced ovulatory disturbances during the pandemic compared to just one in 10 women from a similar study conducted over a decade ago, clinicians say.

“These silent ovulatory disturbances likely explain why so many women who are not taking hormonal forms of birth control reported having early or unexpected periods in the days following a COVID-19 vaccination,” said study author and Canadian endocrinologist Dr Jerilynn Prior.

The findings from the Menstruation Ovulation Study 2 (MOS2) were presented at the Endocrine Society’s annual meeting, ENDO 2022, in the US earlier this month.