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Most Studies Show COVID Vaccine Affects Menstrual Cycles, BMJ Review Finds



Women experienced menstrual cycle disruption following COVID-19 vaccination, including changes in cycle length, flow and menstrual pain, according to a new “state of the science” review published Monday in BMJ Sexual & Reproductive Health.

Although women comprised about half of the participants in the original COVID-19 vaccine trials, no data were collected on how the shots affected their menstrual cycles.

Soon after the shots were rolled out, many women started reporting longer periods and heavier-than-normal bleeding, and many women who did not normally menstruate — including women on long-acting contraceptives and post-menopausal women — also reported unusual bleeding.

Tens of thousands of women reported symptoms to researchers and medical regulators in the U.S. and the United Kingdom respectively by mid-2021.

At the time, women’s concerns were often “blown off” and they felt “gaslighted,” Dr. Alison Edelman, one of the review article authors, told NBC.

Researchers called for studies into the issue, in part because they said disrupted menstrual cycles were driving “misinformation” that the vaccines were dangerous and fueling “vaccine hesitancy.”

Since then, dozens of studies have been published on the issue.

For the BMJ review, researchers from Harvard, Boston University, Michigan State University and Oregon Health & Science University surveyed and summarized the existing published literature in the PubMed database — which contains peer-reviewed research in the biomedical and life sciences literature — on the COVID-19 vaccines and menstruation.

“Overall, data from published studies indicate small transient changes in menstrual cycle length (ie, longer cycle length) following vaccination,” they concluded.

“Additionally, there is some evidence that other menstrual characteristics such as menstrual pain, menstrual flow and intermenstrual bleeding also occur following vaccination.”

Because there is more limited research, less is known for certain about the shot’s effects on specific age groups, such as adolescents or post-menopausal women. However, data suggest that breakthrough bleeding or menstrual cycle changes affect them, they wrote.

Evidence also suggests the menstrual cycle phase a woman is in at the time of vaccination may play a role in how vaccination affects menstruation, the researchers said.

Assessing the effects of COVID-19 vaccination on menstrual cycles is important, because the menstrual cycle is a significant indicator of women’s health, and research suggests there is a major gap in understanding, they said.

However, the lack of standardized measures for assessing menstrual-related issues makes it challenging to summarize the data, they wrote, so many of the studies did not necessarily measure the same outcomes…


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