Scientists from the University of Edinburgh found that the COVID-19 vaccine did not cause significant changes in the menstrual cycle. Research published in the journal iScience.
The authors reviewed the results of a survey conducted in the UK in March 2021. Nearly 5,000 women who received the COVID-19 vaccine attended the event.
82% reported no menstrual cycle changes. Only 6.2% reported significant discomfort, 1.6% reported mild discomfort, and another 10.2% reported other changes in the length, regularity, or amount of menstrual bleeding.
Of the 18% who reported changes, the risk was higher among women who smoked, had a history of COVID-19, or did not use estradiol-containing contraception.
The researchers then looked at a larger group of 12,000 women, including vaccinated and unvaccinated women.
Compared to those who were not vaccinated and had no COVID-19, those who were vaccinated did not report more frequent menstrual irregularities. Those recovering from COVID-19 were more likely to report heavier bleeding, missed periods, and bleeding between periods.
The scientists hope the results will help clinicians advise women about the relative risks of menstrual irregularities from the COVID-19 vaccine relative to the infection itself, and help women make decisions about getting the COVID-19 vaccine.