NIH study confirms that covid vaccination causes a slight increase in menstrual cycle.

On January 26, 2022, a healthcare worker at a vaccination clinic in the Peabody Institute Library in Peabody, Massachusetts, United States, administers a dosage of the Pfizer-BioNTech Covid-19 vaccine to a patient.

Reporting by Vanessa Leroy; Photography by Bloomberg/Getty Images

According to a big worldwide study supported by the National Institutes of Health, immunisation against covid-19 causes a modest increase in the length of a woman’s menstrual cycle by delaying the onset of bleeding by a few hours.

Vaccination-related alterations appear modest, transient, and within the usual range, according to Dr. Diana Bianchi, director of the National Institutes of Health’s Child Health and Human Development Institute. However, the health ministry found that the longer menstrual cycle, which is normally around a month long, did not necessarily increase the number of days of bleeding.

According to NIH guidelines, a shift of eight days or less in menstrual cycle duration is within the acceptable range of variation. With the initial vaccination, participants’ menstrual cycles lengthened by an average of.71 days, or less than 24 hours; following the second vaccination, they lengthened by a little more than half a day. Women who received both doses of the vaccination during the same menstrual cycle experienced a 3.91-day increase in the length of their cycles.

However, 6.2% of vaccinated individuals and 5% of unprotected persons in the research reported an increase of eight days or more in their cycle. The delay in the onset of menstruation was greater in younger women who had longer cycles prior to immunisation.

Women who received one dosage each menstrual cycle saw a return to normal cycle length when the vaccine series was complete, but those who received both doses in a single cycle saw a reduction in cycle duration of roughly 20 hours.

Nearly 20,000 participants from Canada, the United Kingdom, the United States, Europe, and other regions of the world took part in the study. Pfizer-BioNTech, Moderna, Johnson & Johnson, AstraZeneca, Covishield, Sputnik, Covaxin, Sinopharm, and Sinovac were among the nine vaccine manufacturers used in the study.

There was no significant variation amongst vaccines in terms of effects on menstrual cycle duration.

The study relied on information collected by the Natural Cycles fertility tracking app. Women logged data such as their body temperature and the duration of their menstrual cycles into the app. There’s an option in the app where users can consent to having their data used for scientific study without giving up any identifying information.

The study published this week verified the association between Covid immunisation and longer menstrual cycles, which had been suggested by preliminary findings disclosed by the researchers in January. To look into the matter, the NIH gave $1.67 million to five different research institutions.

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