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Weak associations were observed between vaccination for COVID-19 and healthcare contacts related to menstrual disturbance or bleeding disorders in women before and after menopause, according to a Swedish register-based cohort study.

Looking at over 2.5 million women who received at least one dose of COVID vaccine, the strongest association for menstrual disturbance observed was an adjusted 26% increased risk among women ages 12 to 49 in the 1-7 days risk window after the first dose (HR 1.26, 95% CI 1.11-1.42), reported Rickard Ljung, MD, PhD, MPH, of the Swedish Medical Products Agency in Uppsala and the Karolinska Institutet in Stockholm, and colleagues.

For premenopausal bleeding, only non-significant associations were observed -- a 14% increased risk in the 1-7 days risk window after the first and third doses.

Among postmenopausal women, the highest risks for bleeding were observed after the third dose, both in the 1-7 days risk window (HR 1.28, 95% CI 1.01-1.62) and in the 8-90 days risk window (HR 1.25, 95% CI 1.04-1.50), according to the findings in .

There was a 23% to 33% increased risk of postmenopausal bleeding after 8-90 days with the Pfizer-BioNTech vaccine, and with the Moderna vaccine after the third dose, but the association with the Oxford-AstraZeneca vaccine was less clear.

"Weak and inconsistent associations were observed between SARS-CoV-2 vaccination and healthcare contacts for bleeding in women who are postmenopausal, and even less evidence was recorded of an association for menstrual disturbance or bleeding in women who were premenopausal," Ljung and co-authors concluded. "These findings do not provide substantial support for a causal association between SARS-CoV-2 vaccination and healthcare contacts related to menstrual or bleeding disorders."

Ljung told 木瓜直播 that "it's important to remember that we do not say that women don't experience these conditions. What we do say is that even if they experience them, they do not seem to be so severe that a woman will seek medical attention for these problems."

"There are a lot of spontaneous reports from women all around the world who have reported suspected adverse events to their drug agencies," he added. "And in Sweden, we have 1,000 of those reports where women have reported that they suspect an adverse event of menstrual disorders or bleeding after vaccination -- but that's self-reported data to the agencies."

Other studies have shown that women have reported slightly longer menstrual cycles following COVID vaccination, and others have reported changes in menstrual symptoms after COVID infection.

Becky Smullin Dawson, MPH, PhD, of Allegheny College in Meadville, Pennsylvania, told 木瓜直播 that the study checks the boxes for rigorous, valid, and reliable data that included very little loss to follow-up in a huge cohort. Her reservations stem from the actual questions the study sought to answer.

"The challenge that I'm struggling with right now is that the things that they were looking for, like irregular bleeding in women who menstruate -- that's not something that most of us go to a doctor for," said Dawson, who was not involved with the study.

She pointed out that the study doesn't answer the more valuable question of whether the COVID vaccine and boosters increase or cause menstrual disturbance, and why.

"Should we be making decisions or making conclusions about the impact of the vaccine just looking at healthcare records for something that I don't think a lot of women go to healthcare facilities for?" Dawson said. "I don't think [this study] changes public health messaging or clinical health messaging."

Ljung said future research should link self-reported questionnaires with health data on the topic to get the best of both worlds.

For this study, the researchers analyzed data from 2,946,448 Swedish women ages 12 to 74 (median age 44) from December 2020 to February 2022. Women who were pregnant, living in nursing homes, or who had a history of menstrual or bleeding disorders, breast cancer or a form of genital-related cancer, or who had a hysterectomy were excluded from the study.

Most women in the cohort (87.6%) received at least one vaccination, and 64% received three doses by the end of the follow-up period.

Covariates included country of birth, age, marital status, education, frequency of prior healthcare visits, and if they were a healthcare worker.

More than 99% of menstrual-related visits were outpatient specialist care appointments.

Ljung and colleagues noted that their dataset did not indicate whether a doctor's visit was planned or acute, which is a limitation to the study. They also pointed out that the time between onset of symptoms and actually interacting with the healthcare system could be "considerable, making the interpretation of effect of different risk windows challenging."

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