When compared to uninfected women, women who received one dose of COVID-19 vaccination during a single menstrual cycle experienced a nearly one-day increase in cycle length.
The lengthening of the cycle (the period between bleeding) was not linked to a change in the number of days between menses (days of bleeding).
The research was published in the ‘Obstetrics and Gynecology Journal.’
The researchers, led by Alison Edelman, M.D., M.P.H. of Oregon HealthScience University in Portland, noted that menstrual cycles normally fluctuate a tiny bit from month to month, and the rise they observed was within normal fluctuation.
They went on to say that more research is needed to see if the COVID-19 vaccine can affect other menstrual characteristics, such as related symptoms (pain, mood swings, etc.) and bleeding characteristics (including heaviness of flow).
“It’s heartening that the study identified only a minor, transient shift in women’s menstrual cycles,” said Diana W. Bianchi, M.D., director of the Eunice Kennedy Shriver National Institute of Child Health and Human Development at the National Institutes of Health (NICHD).
“For the first time, these findings allow us to counsel women about what to expect from COVID-19 vaccination so that they may plan properly,” she added.
Dr. Bianchi went on to say that little research has been done on how COVID-19 immunizations, or vaccines for other diseases, can affect the menstrual cycle.
The researchers looked at de-identified data from Natural Cycles, a fertility tracking app. Users provide information on their body temperature and menstrual cycles, and they can choose to have their de-identified data used for research. The data for vaccinated individuals came from three consecutive cycles before vaccination and three more consecutive cycles after vaccination, including the vaccination cycle or cycles.
For unvaccinated people, data was collected for six cycles in a row. 2,403 of the 3,959 people in the research were vaccinated, while 1,556 were not.
Pfizer and Moderna vaccines were given to the majority of those who were vaccinated. The first immunization dosage was linked to a.71-day increase in cycle duration, while the second dose was linked to a.91-day increase.
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As a result, users who were vaccinated twice saw an increase of less than one day in each vaccination cycle. The number of monthly bleeding days for the vaccinated people did not vary. The unvaccinated app users’ cycle length did not change significantly, according to the study.
A subgroup of app users (358 users) who received two vaccine doses during the same menstrual cycle experienced a two-day increase in cycle length. This difference appeared to diminish in consecutive cycles, indicating that the menstrual changes are most likely transient.
The International Federation of Gynecology and Obstetrics classifies a shift in cycle length as normal if it is less than eight days, according to the authors. (ANI)