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  • New research finds that getting the COVID-19 vaccine is unlikely to irregular periods.
  • The study authors looked at millions of women both pre and postmenopausal to see if the COVID-19 vaccine could affect menstruation or bleeding risk.
  • Researchers said especially in premenopausal women there was no association of increased risk of irregular periods.

In the early days of the COVID-19 vaccination campaign, there was concern that the vaccine may have an effect on some women’s menstruation cycles.

However, the latest study, published in the BMJ and led by researchers at the Swedish Medical Products Agency, shows that there is no strong association between the COVID-19 vaccines and changes in menstruation.

The study authors looked at millions of women both pre and postmenopausal to see if the COVID-19 vaccine could affect menstruation or bleeding risk.

“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,” the study authors wrote.

This most recent BMJ study looked at medical records from nearly 3 million Swedish women between the ages of 12 and 74, particularly those who visited healthcare professionals because of menstrual changes between December 2020 and February 2022. Contact with healthcare included primary care visits, specialist outpatient visits, and days of hospital stay related to menstrual disturbance or bleeding before or after menopause.

The study found that it is a weak and inconsistent association between vaccination and contact with healthcare for postmenopausal bleeding and even less consistent for menstrual disturbance and bleeding in those who were premenopausal.

“There is an association and it’s weak, and I think that it seems to be less dire than the information we got out of the United States,” said Dr. Jennifer Wu, an OB/GYN with Lenox Hill in New York. “This data tells us that people should not be discouraged from the vaccine because of menstrual irregularities.”

The new study comes to a different conclusion than earlier research. In that early research, experts found signs that there was a link between the COVID-19 vaccine and changes in menstrual cycles. However, those studies had certain limitations including a limited pool of participants and not controlling for other factors such as COVID-19 hospitalization that could impact menstrual irregularities. Other factors like stress and depression have an effect on the menstrual cycles, and many people during the pandemic were experiencing new symptoms of both stress and depression.

In the latest study, more than 2.5 million (88%) of women received at least one COVID-19 vaccine and more than 1.6 million (64%) of vaccinated women received three doses during the study period.

“This new research from Sweden is amazing in that it’s a national registry and the data is very clean,” said Wu. “It’s free of bias. They do not have such large registries in the U.S., where we have different insurances in different states and things like that.”

Menstrual irregularities refer to if the length of the menstrual cycle, or the gap between periods, keeps changing, meaning your periods come early or late. The average menstrual cycle is 28 days, but it’s not uncommon for it to be shorter or longer than this, and that could be for many reasons.

There are many factors that can lead a woman to experience an irregular period including:

  • Hormone imbalances
  • Medical conditions including endometriosis and pelvic inflammatory disorder
  • Medications
  • Benign growths or cancer.

It is not uncommon for premenopausal women to experience period irregularities.

“It can be as simple as your period coming a week early, or having two periods in a month, or maybe coming a week late,” said Wu. “This is not a huge cause for concern in someone of childbearing age. It can happen for so many reasons and that can be why women are less likely to report that to a registry and then seek a medical appointment for it. It’s so common, so they may not even really note it.”

What the study did find is that the highest risks for bleeding in postmenopausal women were seen after the third dose in the 1-7 days risk window and in the 8-90 days risk window. But the issue of who reports what to healthcare professionals should be taken into consideration here, as well.

“Someone who is postmenopausal and starts bleeding is much more likely to contact their doctor than someone who is young and has a bit of abnormality in their menses,” said Wu. “In that way, I think that’s what you have to look at with the two populations. I think it’s a reporting difference.”

In premenopausal women, the associations were weak for menstrual disturbance or bleeding after vaccination with any dose.

“[This new research] is a clarification because there were a lot of case reports of menstrual irregularity with the vaccine and it seemed more serious and more widespread than is presented in this nationwide registry data,” Wu added. “I do not think it is a serious side effect that needs to be highlighted for patients.”

A new study finds there is little evidence that getting the COVID-19 vaccine will lead to periods being irregular.