A new study, first of its kind, has analysed and documented the effects of Covid-19 vaccination on menstrual cycle and has found that in some women it has brought temporary changes in the length of the monthly cycle by altering it by a day.
The study published in the journal Obstetrics & Gynecology was carried on nearly 4,000 US based individuals. So far the effects of the vaccine on the menstrual cycle was known only anecdotally.
What does the study finds
The study analysed women belonging to the age group of 18 and 45 years and having normal menstrual cycles (between 24-38 days) for at least three consecutive cycles before their first dose of vaccination. The data was studied using an application ‘Natural Cycles’
Among the 4,000 women, 2, 402 subjects were vaccinated and 1,500 didn’t receive a single Covid jab. The vaccinated mostly received the Pfizer-BioNTech vaccine (55 per cent) and about 35 per cent received the Moderna vaccine. 7 percent of these women received a Johnson and Johnson Covid jab.
Researchers found that Covid-19 vaccines administered in the US were associated with one up to one day change in cycle length for both vaccine doses compared to pre-vaccine cycles. Lead researcher Alison Edelman said that the study found an average change of less than one day and in some rare instances women who received both doses in the same cycle. These temporary changes get resolved in the next menstrual cycle, she added.
Limitations of the study
The study did not show the vaccine’s impact on the length of the period or bleeding. Moreover, the data of ‘natural cycles’ is not inclusive as most of the US population that uses it are likely to be White, college educated and have Body Mass Index lower than national average and also do not use hormonal contraception techniques.
Since the study analysed only women with normal and consistent menstrual cycles but many women do not fit into the normal category, therefore it cannot be said with certainty if other populations experience similar change in length of cycle.
The study also does not include enough subsequent cycles pre-vaccination to fully understand the vaccinated cohort used for the study.