Study confirms link between COVID-19 vaccination and temporary increase in menstrual cycle length - National Institutes of Health (.gov)

study that linked COVID-19 vaccination with an average increase in menstrual cycle length of less than one day.

Funded by the National Institutes of Health, the new study included data from nearly 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 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., director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD).

NICHD and NIH’s Office of Research on Women’s Health funded the study, which was part of $1.67 million awarded to five institutions to explore potential links between COVID-19 vaccination and menstrual changes.

Although small menstrual changes may not be meaningful to health care professionals and researchers, the study authors wrote, perceived changes in a bodily function linked to fertility may be alarming to those experiencing it and could contribute to vaccine hesitancy.

Participants who received both doses in a single cycle had a 3.91 day increase in cycle length

After vaccination, cycle length had increased by only .02 days for individuals who received one dose per cycle, and .85 days for individuals who received two doses in one cycle, compared to participants who were not vaccinated

Women who were younger and who had longer cycle length before vaccination were more likely to experience the increase

About the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD): NICHD leads research and training to understand human development, improve reproductive health, enhance the lives of children and adolescents, and optimize abilities for all

Association between menstrual cycle length and COVID-19 Vaccination: a Global Cohort. BMJMedicine

Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD)