The study, released Wednesday, followed nearly 4,000 U.S. women through six menstrual cycles, and on average, the next post-injection period began about a day later than usual.
One of the first studies to monitor whether vaccination against COVID-19 could affect menstruation in women revealed a small and temporary change. The study, released Wednesday, followed nearly 4,000 U.S. women through six menstrual cycles, and on average, the next post-injection period began about a day later than usual. But there was no change in the number of days of menstrual bleeding after vaccination against COVID-19.
“This is incredibly encouraging,” said Dr. Alison Edelman from the University of Health and Science in Oregon, who led the research and said that it is important to tell women what to expect. Some women have reported irregular periods or other changes in menstruation after the injection. National Institutes of Health is funding studies to examine whether there is a link.
Edelman’s team analyzed data from a birth control app called Natural Cycles, approved by the Food and Drug Administration for women to monitor their menstrual cycles and say when they are most likely to get pregnant. Menstrual cycles are counted from the first day of one menstruation to the first day of the next. Small variations from month to month are normal, and stress, diet, and even exercise can trigger temporary changes.
Edelman said the study included women with “most normal of normal” cycles, averaging between 24 and 38 days. The researchers followed vaccinated women three cycles before vaccination and the immediate three cycles after, including the months they received the dose – and compared them with unvaccinated women. The application prompted women to enter information about the vaccine.
A subset of 358 women who received both doses of the vaccine in the same menstrual cycle noticed a slightly larger change in the length of the next cycle, averaging two days. About 10% of them had a change of eight days or more, but later returned to normal, the researchers reported in the journal Obstetrics & Gynecology.
Edelman said that one theory is that when the immune system is strengthened at certain moments of the cycle, “our body clock or what controls the menstrual cycle can have hiccups.” bleeding or if women who have irregular periods react differently.
The findings provide “important new evidence highlighting that any impact of the COVID vaccine on menstruation is both minimal and temporary,” Dr. Christopher Zahn of the American College of Obstetricians and Gynecologists said in a statement.
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