There is no evidence of increased risk of menstrual changes after having the COVID-19 vaccine, according to a new Swedish study published today.
Research involving nearly three million women concluded there were weak and inconsistent associations between COVID-19 vaccination and contact with healthcare for postmenopausal bleeding. The association was even less consistent for menstrual disturbance and premenstrual bleeding.
Writing in the latest edition of The BMJ, the authors say their findings do not provide any substantial support for a causal association between COVID-19 vaccination and diagnoses related to menstrual or bleeding disorders.
The research team, which involved the Swedish Medical Products Agency, Uppsala; the Karolinska Institutet; University of Gothenburg; Sahlgrenska University Hospital, Gothenburg; and Uppsala University, drew on high-quality health registry data to evaluate the risks of menstrual disturbance and bleeding after COVID-19 vaccination in 2,946,448 women aged 12-74 years from December 2020 to February 2022.
These included the number of days they bleed and the heaviness of the flow.
The team examined primary care visits, specialist outpatient visits, and days of hospital stay related to menstrual disturbance or bleeding before or after menopause.
Risks were assessed by vaccine – Pfizer-BioNTech, Moderna, or Oxford-AstraZeneca – and dose (unvaccinated and first, second, and third dose) over two times: one-seven days, which was the control period, and eight-90 days.
In the main analysis, more than 2.5 million (88%) of women received at least one COVID-19 vaccination and more than 1.6 million (64%) of vaccinated women received three doses during the study period.
The highest risks for bleeding in postmenopausal women were seen after the third dose in the one-seven days risk window (28%) and in the eight-90 days risk window (25%).
Adjusting for socioeconomic factors, previous healthcare use and for several specific medical conditions had only a modest effect on these results.
Analyses of individual vaccines and risk of postmenopausal bleeding suggested a 23-33% increased risk after eight-90 days with Pfizer-BioNTech, and Moderna after the third dose, but a less clear association with Oxford-AstraZeneca.
In premenopausal women, weak associations were found for menstrual disturbance or bleeding after vaccination with any dose at 13% or 8% after one-seven days and 6% or 1% after eight-90 days, respectively.
However, adjusting for other factors almost completely removed these weak associations, suggesting that a causal effect is unlikely.
Although this is an observational study with some limitations, including the fact that the time between onset, start of symptoms, and date of healthcare contact might be considerable, the authors say it was a large study with near complete follow-up, using mandatory data from nationwide registers.
“We observed weak and inconsistent associations between SARS-CoV-2 vaccination and healthcare contacts for postmenopausal bleeding, and even less consistent for menstrual disturbance, and premenstrual bleeding,” they write.
“These findings do not provide any substantial support for a causal association between SARS-CoV-2 vaccination and healthcare contacts related to menstrual or bleeding disorders.”
Ljung R, Xu Y, Sundström A et al. Association between SARS-CoV-2 vaccination and healthcare contacts for menstrual disturbance and bleeding in women before and after menopause: nationwide, register based cohort study. BMJ 4 May 2023; doi: 10.1136/bmj-2023-074778
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