Lead author Dr Alison Edelman of Oregon Health & Science University recalls that menstrual cycles generally vary slightly from month to month and the observed increase remains within the range of normal variability. However, the team calls for further research to clarify the mechanism by which the COVID-19 vaccination might influence other menstrual characteristics, such as associated symptoms (pain, mood changes, etc.) and bleeding characteristics. . Finally, the researchers specify that the International Federation of Gynecology and Obstetrics considers a variation in cycle length as normal if the change remains less than 8 days.
An increase of 1 day on average in the length of the menstrual cycle
Synthetic, the study shows that women receiving a dose of a COVID-19 vaccine in a single menstrual cycle experienced an increase in cycle length of almost a day, compared to unvaccinated women. However, increased cycle length – a longer period between periods – is not associated with any change in the number of days you get your period.
The study: this is the analysis of anonymized data from a fertility monitoring application, “Natural Cycles”, on 3 consecutive cycles before vaccination and 3 consecutive cycles following vaccination, including the cycle (s) during which vaccination had taken place. In total, these data were analyzed for 3,959 participants, of which 2,403 were vaccinated and 1,556 were unvaccinated. Most of the women vaccinated were vaccinated with the Pfizer and Moderna vaccines. The analysis shows precisely that:
- on average, the first dose of vaccination is associated with an increase in cycle length of 0.71 days;
- the second dose increased by 0.91 days;
- participants vaccinated over 2 cycles experienced an increase of less than one day in each of the vaccination cycles;
- no change was noted in the number of bleeding days in vaccinated women;
- no significant change in cycle length was seen in unvaccinated women.
- a subgroup of 358 participants who received 2 doses of vaccine in the same menstrual cycle experienced a larger average increase in cycle length, estimated at 2 days;
- this change gradually subsided over subsequent cycles, suggesting that these menstrual changes are likely temporary.
The authors want to be reassuring: “The study found only a small, temporary menstrual change in the vaccinated women”, commente le Dr Diana W. Bianchi, directrice de l’Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD/NIH), “These results provide, for the first time, the opportunity to advise women on what to expect from the COVID-19 vaccination”. Overall, adds Dr Bianchi, little research has been done on how COVID-19 vaccines, or other vaccines, can affect the menstrual cycle …
