“My periods are longer. "I'm bleeding more than usual." Since the first vaccines administered against Covid-19, alerts about a change in the menstrual cycle have multiplied on social networks. Leaving doctors sometimes helpless in the face of the lack of scientific data to provide validation of this phenomenon.
To shed some light, a Franco-British study was led by Alexandra Alvergne, researcher at the CNRS. “We had not planned to do a study on the effect of the Covid-19 vaccine on menstrual cycles. But, faced with multiple concerns on social networks and the lack of data, we decided to explore this track, "she explains to Le Point.
This study was carried out using data collected in the United Kingdom from 12,000 menstruating participants, of all ages, with or without children, from all geographical areas, of all socio-economic status, vaccinated or not against Covid-19. “The idea was to have the most representative panel possible of the population in order to limit bias. All of the women completed an online questionnaire.
Thanks to this, the team found that one in five women perceived a change in their menstrual cycle (longer cycle, heavier bleeding, etc.). "According to pharmacovigilance criteria, it is therefore a relatively frequent side effect of vaccination", underlines the researcher. As part of this study, the team also wanted to determine if there were any risk factors. “We found that smoking, having previously been infected with Covid-19 increased the risk of observing changes in one's menstrual cycle after vaccination. Conversely, using a hormonal contraceptive that contains estrogen represented a protective factor,” summarizes Alexandra Alvergne. These findings were published in the journal iScience.
Additionally, scientists wanted to determine if these changes could be serious for women's health. “With objective scientific criteria established by the International Federation of Gynecology and Obstetrics, we found that there was no link between vaccinated women and the development of abnormal parameters. Having a cycle less than 24 days or more than 38, having a cycle length difference of more than 9 days or periods longer than 8 days are abnormal situations,” explains the researcher. Before qualifying: "Yes, women experience cycle changes, but these changes are not of medical concern. »
These changes therefore appear as a mild side effect of vaccination, such as pain at the injection site. “This change is not serious and everything usually returns to normal by the next cycle. It is a temporary effect. Given the current data, this change should not be alarmed. The same effects were noticed regardless of the vaccine used against Covid-19.
Finally, avenues are discussed to understand this possible modification. “The most likely explanation is that the immune response induced by the vaccination leads to inflammation of the endometrium, the lining that lines the uterus, thus causing certain changes in the cycle. However, we did not find that women with endometriosis or polycystic ovary syndrome had more dysregulation than those without. Other studies have reported changes in cycle length, but minor and temporary changes as well.
