COVID Vaccine May Temporarily Add 1 Day to Menstrual Cycle: Study

Written by Amy Norton HealthDay Reporter >

Friday, January 7, 2022 — Vaccination against COVID-19 may slightly and temporarily lengthen the time between women’s menstrual periods, a new study says.

On average, the researchers found the extra time to be just under a day. They said it’s something not many women will notice and is nothing to worry about from a health point of view.

But it confirms reports from some women that after being vaccinated against COVID, their menstrual cycle in that month was different.

“I think these findings are reassuring, and they also validate what people are reporting,” said lead researcher Dr. Alison Edelman, professor of obstetrics and gynecology at Oregon Health & Science University in Portland.

It’s not surprising, in fact, that vaccination may affect a woman’s menstrual cycle, Edelman explained, because there are links between the immune system and menstruation.

COVID-19 vaccines block a strong and desirable immune response. As part of this, the body produces cytokines – small proteins that stimulate the immune system to fight foreign invaders.

But Edelman said cytokines can also affect the internal “clock” that keeps various body processes running on schedule. So it makes sense that the timing of a woman’s menstrual cycle might be a bit overlooked that month.

However, Edelman said, there has been very little research into how vaccines in general affect women’s cycles.

“Where there is a dearth of information, there is misinformation,” said Candace Tengen of the branch of gynecology and women’s health at the National Institute of Child Health and Human Development in Bethesda, Maryland.

The Federal Institute funded the study as part of a larger project looking at the links between the COVID vaccine and menstrual cycle changes.

Tingen said the goal is to fill in the knowledge gaps and give women better information before vaccination. During the coronavirus vaccination campaign, some women have reported changes in their periods that they believe are linked to the shots — whether on social media or, in a few cases, the federal government’s vaccine adverse event reporting system.

But Tengen said menstrual cycle changes were not monitored during clinical trials of the vaccines.

For the new study, published Jan. 5 in the journal Obstetrics and gynecologyResearchers analyzed anonymous data from a fertility tracking app. Users enter information about their menstrual cycles and can consent to it being used for research purposes.

Edelman’s team focused on just under 4,000 women, about 2,400 of whom have been vaccinated against COVID (most with Moderna or Pfizer).

Compared to the three months before the vaccination, these women had a slightly longer menstrual cycle after the first and second vaccine doses: less than a day longer, on average.

This means more time between periods. The women did not have any additional days of bleeding. In contrast, non-immunized women showed no change in average cycle length over five months.

According to Edelman, this type of variation in cycle length falls within the range considered “normal,” which is less than eight days.

“Most women probably won’t notice a change for less than a day,” Tingen said. But she noted that this is the average in this study, which means the delay will be a little longer for some women.

That may be a concern for some, Tingen said.

She agreed that given the links between the immune system and menstruation, including some “common chemicals,” it makes sense that vaccination could temporarily disrupt women’s cycles.

And now, with some data in hand, women can be told that a COVID shot may delay their next cycle a bit.

The study only looked at menstrual length, not other types of changes in the menstrual cycle, such as heavy bleeding. Both Tingen and Edelman said the findings do not address COVID-19 vaccination and fertility.

This is an area where misinformation abounds. But Tengen said all the data the researchers had collected at this point was reassuring: There is no evidence that vaccinating against the coronavirus makes pregnancy more difficult.

© 2022 HealthDay. All rights reserved.

More support and information about COVID-19

Leave a Comment