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Covid Vaccination’s Association With Increase In Menstrual Cycle Length: Study

The researchers noted that changes in cycle length did not vary concerning the kind of vaccine taken. Moreover, an alteration in cycle length of fewer than eight days is considered within the normal range of variation, they added

COVID-19 shorts are related to an average increase in menstrual cycle length of less than one day, said a study by researchers from Oregon Health & Science University which was published in the British Medical Journal.

The researchers found a 0.71 day increase after the first vaccine dose and a 0.56 day increase after the second shot, whereas women who took both doses in a single cycle experienced a 3.91 day increase in cycle length.

The researchers noted that changes in cycle length did not vary concerning the kind of vaccine taken. Moreover, an alteration in cycle length of fewer than eight days is considered within the normal range of variation, they added.

After vaccination, cycle length had increased by only 0.02 days for individuals who received one dose per cycle and by 0.85 days for those who received both doses in one cycle, compared to participants who had not been vaccinated.

Even as the minute menstrual changes may not be meaningful to health care professionals and researchers, the perceived alteration in a bodily function associated with fertility might seem alarming to those experiencing it, which might lead to their vaccine hesitancy, noted the study authors.

Overall, 19,622 individuals participated in the large, international study, out of which 14,936 were vaccinated and 4,686 were not. The researchers examined data on at least three successive cycles before vaccination and at least one cycle after. Data from at least four consecutive cycles was examined for a similar span of time for unvaccinated participants. Out of the total participants, 1,342 experienced variations in cycle length of eight or more days, comprising 6.2 per cent of vaccinated individuals and 5 per cent of unvaccinated individuals.

Younger women with longer cycle lengths before vaccination were found to be more likely to experience an increase in cycle length. The fertility tracking app, Natural Cycles, was used by researchers to analyse de-identified data.

Users of the app provided information on their temperatures and their menstrual cycles. The worldwide rollout of COVID-19 vaccines allowed the study authors to expand on their original study of people in the US.

The study comprised data from participants throughout the world, but mainly from the UK (32 per cent), the US and Canada (29 per cent) and Europe (34 per cent). Apart from the messenger RNA Covid-19 vaccines (Pfizer-BioNTech and Moderna), participants received vaccines made from engineered viruses (AstraZeneca, Covishield, Johnson & Johnson, and Sputnik), and inactivated viruses (Covaxin, Sinopharm, and Sinovac).



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