One of the first studies to track the impact of the COVID-19 vaccine on women’s menstrual cycles ahead of time found mild and temporary changes. For this reason, additional research was conducted to verify the results obtained. Newly presented in this year’s January issue of Obstetrics & Gynecology. It involved 4,000 US women whose menstrual cycles were analyzed over six months. The data came from a birth control app called Natural Cycles. This application is approved by the US Food and Drug Administration. Researchers at Oregon Health & Science University note that menstruation after a vaccination against COVID-19 starts about a day later than usual. A change in the number of days of menstrual bleeding, however, was not observed. Menstrual cycles are counted from the first day of one period to the first day of the next. Slight variations from month to month are normal. Causes of temporary changes can be stress, diet, and even exercise. The study included women with a regular menstrual cycle, the duration of which averaged between 24 and 38 days. The researchers followed the vaccinated women for three cycles before vaccination and the immediate three cycles after, including the months in which they received a dose of the vaccine. They compared the duration in unvaccinated women. In 358 of the women who received both doses of the vaccine, there was a slightly greater change in the length of their next period, an average of two days. About 10% of them had a greater change – eight days or more – but subsequently returned to normal ranges. From the information obtained, it is concluded that the possible impact of the vaccine against COVID-19 on the menstrual cycle is minimal and temporary. Sources: https://journals.lww.com/greenjournal/Fulltext/9900/Association_Between_Menstrual_Cycle_Length_and.357.aspx