Various studies have shown that the SARS-CoV-2 vaccine can increase the duration or bleeding of the menstrual cycle. Now, a new study concludes that if vaccination is done after ovulation (luteal phase), side effects can be reduced. This study, carried out by researchers from the Artificial Intelligence Research Institute (IIIA-CSIC), the University of Geneva, the Hospital de la Santa Creu y Sant Pau and the Agència de Qualitat i Avaluació Sanitàries de Catalunya (AQuAS), has been published in the American Journal of Obstetrics and Gynecology.
Half of the women surveyed in a study had alterations of the menstrual cycle after the COVID vaccine
The research is based on data from more than 1,800 cycles of 371 women collected by the App Lunar menstrual cycle monitoring application. The clinical part of this information was reviewed by gynecologists from the Santa Creu and Sant Pau hospitals, while the IIIA researchers looked for common patterns in these data. This app incorporated a new functionality: the dose, brand and the country in which the vaccine had been received could be registered.
Among their users, they chose 371 anonymous profiles who registered at least five consecutive menstrual cycles, and who at the time of vaccination were in the third cycle. In total, 1,855 cycles were recorded between September 2020 and February 2022. The women indicated the cycle length, length of the menstruation period, and variations in bleeding and pain intensity.
The results were then screened according to the phase of the cycle in which the users had been vaccinated.
“It was observed that people who had been vaccinated during the follicular phase, that is, before ovulation, presented an average increase in cycle length of one day, while people who had been vaccinated during the luteal phase did not present any increase”, highlights Borja Velasco, coordinator of the project and researcher at the IIA-CSIC and at AQuAS.
Among users vaccinated in the follicular phase, 11% experienced an increase in menstrual cycle length of more than 8 days, a clinically significant value.
The study highlights the importance of the phase of the menstrual cycle at the time of vaccination to minimize alterations in said cycle, and concludes that vaccination during the luteal phase would avoid the potential increase in the length of the menstrual cycle.
These results, observed in the different types and brands of vaccines, are part of “an important and new topic, on which there is still little evidence. Without the wake-up call of so many menstruating people reporting these changes, studies like this would not be done,” he concludes.