COVID-19 vaccine generates a small and temporary change in the menstrual cycle

In one of the first studies to analyze whether the vaccine against COVID-19 affects the menstrual periods of women, a small and temporary change is observed.

Research published Wednesday followed nearly 4,000 women in the United States for six menstrual cycles and, on average, from the injection, the next period started about a day later than usual. However, there was no change in the number of days of menstrual bleeding after vaccination.

“This is very reassuring,” said Dr. Alison Edelman of the Oregon Health and Science University, who led the research. She added that it is important to inform women of what to expect.

Many women have reported irregular periods or other menstrual changes after getting vaccinated against COVID-19. The National Institutes of Health is funding studies to examine whether there is any link.

Edelman’s team analyzed the data through a contraceptive app called Natural Cycles, approved by the Food and Drug Administration (FDA) that allows women to track their menstrual cycles and know when it is. more likely to get pregnant.

Menstrual cycles are counted from the first day of one period to the first day of the next. Slight variations from month to month are normal, and stress, diet, and even exercise can cause temporary changes.

Edelman explained that the study included women with a cycle length “as normal as normal,” averaging between 24 and 38 days.

The researchers followed the vaccinated women for three cycles before receiving the vaccines and the three immediate cycles after, including the months they received a dose, and compared them to the unvaccinated women. The app asked participants to enter information about the vaccine.

A subgroup of 358 women who received both doses of the vaccine in the same menstrual cycle experienced a slightly greater change in the length of their next cycle – two days on average.

10% of them had a change of eight days or more, but then returned to normal ranges, the researchers reported in the journal Obstetrics & Gynecology.

One theory, according to Edelman, is that when the immune system speeds up at certain times in the cycle, “our biological clock, or what controls the menstrual cycle, can be disrupted.”

The doctor plans to conduct additional studies to see if there are changes in the intensity of menstrual bleeding or if women who have irregular periods react differently.

The results provide “important new evidence highlighting that any impact of COVID vaccines on menstruation is minimal and temporary,” said Dr. Christopher Zahn of the American College of Obstetricians and Gynecologists in a statement.