Many women vaccinated against COVID-19 notice slight changes in their menstrual cycle. What are they and what can they result from? The latest research on the subject has just been published in Obstetrics & Gynecology.
There has been talk of menstrual cycle disorders after vaccination for COVID-19 for some time - menstruating and vaccinated women report to gynecologists, among others more abundant menstruation and the presence of clots, as well as changes in the date of the menstruation itself. The authors of this latest study looked at the length of the menstrual cycle in women before and after vaccination, looking at both menstrual delays and the duration of menstruation.
The analysis included almost 4,000 menstruating women in the US, aged 18-45, who usually had a cycle of 24-28 days - anonymous data from the "Natural Cycles" application that tracks fertility in women not using hormonal contraception. The number of vaccinated women was approximately 2,400 (the study included women vaccinated with Pfizer, Moderna and Johnson & Johnson).
Data from vaccinated women were analyzed for three consecutive cycles prior to the first dose of vaccine, and then for three cycles after vaccination. The data of unvaccinated women (approx. 1,500 people) were analyzed in six consecutive cycles.
Researchers found that after the first dose of the vaccine, the menstrual cycle increased by an average of 0.64 days, and after the second - by 0.79 days (comparing data from the vaccinated and unvaccinated groups).
The study's lead author, Alison Edelman of Oregon He alth & Science University told AFP that the changes were minor and possibly temporary. Commenting on these results, the researcher added that the slight increase in the length of the menstrual cycle is not clinically significant, and any cycle change lasting less than eight days is classified as normal by the International Federation of Gynecology and Obstetrics.
According to the researchers, the changes in the cycle are most pronounced when vaccination occurs in the early follicular phase, starting on the first day of bleeding and ending with the onset of ovulation. This would be suggested by the cases of women who received the first and second doses of mRNA vaccines at this stage, and whothe cycle was extended by an average of two days.
Researchers suspect that the changes in menstrual cycle length following COVID-19 vaccination are likely due to a transient immune system response to the vaccine. The vaccine mobilizes the immune system to react to the presence of foreign proteins, and transient inflammation affects the menstrual cycle. A similar phenomenon occurs with other vaccines such as typhoid and hepatitis B.