No Solid Evidence of COVID-19 Vaccination Leading to Menstrual Changes, Asserts Recent Study

A study conducted in Sweden involving almost 3 million women found no strong evidence associating COVID-19 vaccination with increased risks of menstrual changes or bleeding disorders. While some weak and inconsistent connections between postmenopausal bleeding and vaccination were acknowledged, these correlations faded upon factoring in other considerations.

Based on data from close to 3 million women, experts suggest that it is unlikely that a causal effect exists. The research, recently published in The BMJ, reinforces this view.

The investigation brought to light a weak and inconsistent link between postmenopausal bleeding and the COVID-19 vaccine, with the relationship between premenstrual bleeding or menstrual disturbances and the vaccine proving to be even more inconsistent.

The researchers maintain that these results do not significantly endorse a causal relationship between COVID-19 vaccination and menstrual or bleeding disorder diagnoses.

Many women have noted alterations in their menstrual cycles following COVID-19 vaccination, including changes in bleeding duration and intensity. While self-reporting may shed light on experiences that may not lead to healthcare contact but might still be distressing to the women involved, conclusions drawn from such reports can be unreliable.

In response, Swedish researchers leveraged robust health registry data to analyze the risks of menstrual disturbances and bleeding following COVID-19 vaccination among 2,946,448 women aged 12-74 years, from December 2020 to February 2022.

Included in the healthcare contacts were primary care visits, specialist outpatient appointments, and hospital stays related to pre- and post-menopausal menstrual disturbance or bleeding.

The researchers evaluated risks based on the type of vaccine (Pfizer-BioNTech, Moderna, or Oxford-AstraZeneca) and dosage (unvaccinated, and first, second, and third doses) across two periods (1-7 days, as a control period, and 8-90 days).

In their primary analysis, over 2.5 million (88%) of the women had received at least one COVID-19 vaccine dose, with over 1.6 million (64%) having received three doses during the study period.

The most significant bleeding risks in postmenopausal women were observed after the third dose in both the 1-7 days risk window (28%) and the 8-90 days window (25%). Adjustments for socio-economic factors, prior healthcare usage, and several specific medical conditions had only a minor impact on these findings.

Upon evaluating individual vaccines and the risk of postmenopausal bleeding, the study indicated a 23-33% increased risk after 8-90 days with Pfizer-BioNTech and Moderna’s third dose, but a less discernible association with Oxford-AstraZeneca.

In premenopausal women, weak associations were found for menstrual disturbance or bleeding after any vaccination dose (13% or 8% after 1-7 days and 6% or 1% after 8-90 days, respectively). However, when adjusted for other factors, these weak associations almost entirely vanished, indicating an unlikely causal effect.

The authors recognize several limitations in these observational findings, such as the significant time between symptom onset, the beginning of symptoms, and the date of healthcare contact, which could complicate the interpretation of the effect of different risk windows.

Despite these limitations, the large-scale study, supported by mandatory nationwide register data, observed weak and inconsistent links between SARS-CoV-2 vaccination and healthcare contacts for postmenopausal bleeding and menstrual disturbances.

In summary, the authors conclude: “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.”

The study, titled “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,” was conducted by Rickard Ljung, YiYi Xu, Anders Sundström, Susannah Leach, Ebba Hallberg, Maria Bygdell, Maria Larsson, Veronica Arthurson, Magnus Gisslén, Rolf Gedeborg, and Fredrik Nyberg, and published on May 3, 2023, in The BMJ.

The SciLifeLab National Covid-19 Research Program, financed by the Knut and Alice Wallenberg Foundation, and the Swedish Research Council funded the study.

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More about COVID-19 Vaccination Menstrual Changes

• The BMJ Journal
• SciLifeLab National Covid-19 Research Program
• Knut and Alice Wallenberg Foundation
• Swedish Research Council