Short-term increase in menstrual cycle length related to COVID-19 vaccination

A recent study found that women who received any type of COVID-19 vaccination had a short-term increase in menstrual cycle length, according to a press release from NIH.

This was the second NIH-funded study to investigate the relationship between menstrual cycle duration and COVID-19 vaccination.

In a large international study, the results of which were published in BMJ Medicine, researchers evaluated 19,622 women — 14,936 vaccinated and 4,686 not vaccinated — to observe if any of the nine COVID-19 vaccines were linked to an increase in menstrual cycle length.

According to the release, researchers obtained data through a fertility tracking app (Natural Cycles) and evaluated data from no less than three successive cycles before vaccination and at least a single cycle after vaccination.

Researchers found that vaccinated women experienced a 0.71-day increase after their first dose; after their second dose, a 0.56-day increase was observed. A 3.91-day increase was found in women who received two vaccine doses within a single cycle, according to the release.

However, in the cycle after vaccination, the increase in length went down for most women. According to the release, women who received one dose during a single cycle had an increase of 0.02 days, and women who received both doses in a single cycle experienced an increase of 0.85 days.

“These findings provide additional information for counseling women on what to expect after vaccination,” Diana Bianchi, MD, director of NIH’s Eunice Kennedy Shriver National Institute of Child Health and Human Development, said in the release. “Changes following vaccination appear to be small, within the normal range of variation, and temporary.”

References:

• Edelman A. BMJ Med. 2022;doi:10.1136/bmjmed-2022-000297.
• Study confirms link between COVID-19 vaccination and temporary increase in menstrual cycle length. https://www.nih.gov/news-events/news-releases/study-confirms-link-between-covid-19-vaccination-temporary-increase-menstrual-cycle-length. Published Sept. 27, 2022. Accessed Sept. 27, 2022.