Premenstrual and menstrual changes reported after COVID-19 vaccination: The EVA project.

Background: Menstrual disorders were not reported as a possible secondary effect in any of the clinical trials for the SARS-CoV-2 vaccines.
Aim: To describe the prevalence of perceived premenstrual and menstrual changes after COVID-19 vaccine administration.
Design: Cross-sectional study.
Methods: A total of 14,153 women (mean age 31.5 ± 9.3 years old) who had received the full course of vaccination at least three months earlier were included in this cross-sectional study. Data including the type of vaccine administered, perceived changes in the amount and duration of menstrual bleeding, presence of clots, cycle length, and premenstrual symptoms were collected through a retrospective online survey from June to September 2021.
Results: Of the women who participated in this study, 3136 reported no menstrual changes and 11,017 (78% of the study sample) reported experiencing menstrual cycle changes after vaccination. In summary, women who reported menstrual changes after vaccination were older (overall p  < 0.001) and slightly more smokers ( p  = 0.05) than women who did not report any changes. The most prevalent changes in relation to premenstrual symptoms were increased fatigue (43%), abdominal bloating (37%), irritability (29%), sadness (28%), and headaches (28%). The most predominant menstrual changes were more menstrual bleeding (43%), more menstrual pain (41%), delayed menstruation (38%), fewer days of menstrual bleeding (34.5%), and shorter cycle length (32%).
Conclusion: Women vaccinated against COVID-19 usually perceive mild menstrual and premenstrual changes. Future studies are warranted to clarify the physiological mechanisms behind these widely reported changes.