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Study: COVID Vaccines Linked to Lengthened Menstrual Cycles


Corona Virus Vaccine | Image by Shutterstock

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An international study funded by the National Institutes of Health has supported the findings of a previous U.S. study, which concluded that women who received one dose of a COVID-19 vaccine during a single menstrual cycle experienced an increase in cycle length of nearly one day.

The cycle length increase was not associated with any change in the number of days of menses (days of bleeding).

The new international study included data from almost 20,000 people from Canada, the United Kingdom, the United States, Europe, and other parts of the world who received any of nine different vaccines.

For most study participants, the increase in cycle length was reportedly resolved in the cycle following vaccination.

“These findings provide additional information for counseling women on what to expect after vaccination,” said Diana Bianchi, M.D., in the NIH news release last week. “Changes following vaccination appear to be small, within the normal range of variation, and temporary.”

Dr. Bianchi is the director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).

A change in menstrual cycle length of fewer than eight days is within the normal range of variation, according to the NIH.

There was an average increase of .71 days, less than 24 hours, in participants’ menstrual cycles after the first vaccine dose. The average increase was .56, slightly longer than half a day, for those receiving the second dose. Women who received both vaccine doses in a single menstrual period had an average increase in their cycle by 3.91 days.

Notably, 1,342 participants — comprised of 6.2% of total vaccinated individuals and 5.0% of total unvaccinated persons — experienced a change in cycle length of eight or more days. Women who were younger and who had longer cycle lengths before vaccination were more likely to experience the increase.

Changes in participant cycle length did not differ according to the type of vaccine received.

A total of 19,622 individuals participated in the study. Of these, 14,936 were vaccinated, and 4,686 were not. Most participants were from the United Kingdom (32%), the United States and Canada (29%), and Europe (34%).

The study researchers analyzed data on at least three consecutive cycles. The successive cycles were before vaccination and at least one cycle after. Data from at least four consecutive cycles were analyzed over a similar time interval for unvaccinated participants.

The nine different vaccines that participants received were Pfizer-BioNTech, Moderna, Johnson & Johnson, AstraZeneca, Covishield, Sputnik, Covaxin, Sinopharm, and Sinovac.

The study researchers used data from Natural Cycles, a fertility-tracking app. Women provided data on their temperature and menstrual cycle length to the app. App users can choose an option to provide their information for research purposes, without sharing any personally identifying information.

The researchers released preliminary findings in January that suggest an association between COVID-19 vaccination and increased menstrual cycle length. The international study published this week appeared to confirm that link.

According to the news release, NICHD and NIH’s Office of Research on Women’s Health funded the study. The funding for the study was part of $1.67 million awarded to five institutions to explore possible links and connections between COVID-19 vaccination and menstrual changes.

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Yanah Blayze the AMAZON
Yanah Blayze the AMAZON
1 month ago

So glad I never contracted, so I WILL not submit to vaccinations. I already bleed heavy for 7 days, before / after miscarriage I DO NOT NEED these extra demons on my uterus