Menstrual Changes Following COVID-19 Vaccination: A Cross-Sectional Study.

: Menstrual changes, including altered cycle length and bleeding patterns, have been reported following COVID-19 vaccination. This study aimed to determine the prevalence and types of menstrual changes occurring after COVID-19 vaccination among female students and staff at a university in Saudi Arabia. : A cross-sectional study was conducted among women aged 18-39 years who received at least one dose of a COVID-19 vaccine. Eligible participants, including university students and staff, were recruited between May 2022 and November 2022. Participants completed a questionnaire detailing their sociodemographic characteristics, general medical and reproductive history, and menstrual characteristics before and after vaccination. The prevalence of various menstrual changes (cycle length, bleeding days, flow, and mid-cycle spotting) was calculated. The demographic factors associated with menstrual changes were analyzed using chi-squared tests. : The 472 included participants had a mean age of 20.9 years, and 95.3% were unmarried. Changes in menstrual cycle characteristics after COVID-19 vaccination were reported by 54.7% of respondents overall. The most common change was in cycle length, followed by the number of menstruation days and bleeding flow. Menstrual changes were not associated with age, BMI, occupation, marital status, or medical history. Changes in intermenstrual bleeding were more frequently reported after the third dose of the Pfizer vaccine compared to the Moderna vaccine ( = 0.014). : More than half of the recruited female students and staff reported menstrual changes following COVID-19 vaccination, with altered cycle length being the most common. The potential underlying mechanisms and implications of these menstrual alterations require further investigation. These findings provide evidence of the menstrual side effects of COVID-19 vaccines among women in Saudi Arabia.