Researchers at the University of Edinburgh evaluated whether the COVID-19 vaccine alters the menstrual cycle. Their findings appeared in iScience, a peer reviewed journal.
The team began with a UK survey carried out in March 2021. Almost 5,000 women who had received the COVID-19 vaccine participated in the study.
Most participants, about 82 percent, reported no changes to their menstrual cycle. A minority described various levels of discomfort: 6.2 percent noted significant discomfort, 1.6 percent reported mild discomfort, and 10.2 percent observed other alterations in cycle length, regularity, or the amount of bleeding.
Among the 18 percent who did experience changes, risk factors included smoking, a prior COVID-19 infection, and not using estradiol containing contraception.
The researchers then expanded the analysis to a larger group of 12,000 women, including both vaccinated and unvaccinated individuals.
Compared with unvaccinated women who had not had COVID-19, vaccinated participants did not report more frequent menstrual irregularities. In contrast, those who had recovered from COVID-19 tended to report heavier bleeding, missed periods, and bleeding between cycles.
The investigators hope these results will help clinicians inform patients about the relative likelihood of menstrual irregularities from vaccination in the context of the infection itself, supporting informed decisions about getting the COVID-19 vaccine.