Why You Shouldn’t Worry if the COVID-19 Vaccine Changes Your Menstrual Cycle

Why You Shouldn’t Worry if the COVID-19 Vaccine Changes Your Menstrual Cycle
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According to a new study, some women who get the COVID-19 vaccines can experience a slight delay in their menstrual cycle but it turns out that there is nothing to worry about if that happens to you!

The research founded by the US government involved 4,000 people and was published in Obstetrics & Gynecology.

It also showed that while women’s period may be delayed by about a day, the number of bleeding days will not be affected.

Alison Edelman, the lead author of the research, shared with AFP that the vaccine effects on menstruating people are really small and most likely temporary, something dubbed as “very reassuring” for all those who have already experienced some changes and were concerned about them.

Of course, the study is also beneficial because it contributes to combating anti-vaccine misinformation which has been taking over social media and discouraging people from getting inoculated against the COVID-19 virus.

A slight increase in one’s menstrual cycle length is not something to worry about either since it is not clinically significant.

According to the International Federation of Gynecology and Obstetrics, any change of fewer than 8 days in a person’s menstrual cycle is considered normal.

Menstrual cycles tend to last for around 28 days but the exact number of days is very different from one woman to the other as well as depending on one’s age.

Furthermore, it can even change during more stressful times.

The scientists involved in the study analyzed anonymous data taken from a fertility tracking app and involved women aged between 18 and 45 all of whom were not on any hormonal contraception.

With that being said, around 2,400 participants were vaccinated as follows:

–       55 percent with Pfizer,

–       35 percent with Moderna,

–       7 percent with Johnson & Johnson.

Furthermore, about 1,500 of the total participants were not vaccinated and were included in the control group in order to be able to compare the changes accurately.

Data on the vaccinated group was collected from 3 consecutive cycles before getting vaccinated as well as from 3 more consecutive cycles that occurred during and after receiving the jab.

Of course, data on the unvaccinated group was collected over the same time period, lasting for 6 total consecutive cycles.

The results showed an average 0.64-day increase in cycle length after receiving the first dose of the vaccine and a 0.79-day increase after the second vaccination when compared to the control group (unvaccinated.)

As for what causes such changes, it is believed to be the immune system’s doing.

Edelman explained that “We know that the immune system and the reproductive system are interlinked.”

Sure enough, a revved-up immune system could impact the hypothalamic-pituitary-ovarian axis, something Edelman dubbed as the “highway of how the brain talks to the ovaries, talks to the uterus,” also known as the “body clock.”

The production of inflammatory proteins (cytokines) seems to cause a disruption in the way the axis regulates the menstrual cycle’s timing.

Any changes seem to mostly happen when the vaccination occurs early on in the follicular phase, which begins on the very first day of the period and ends when ovulation starts.

That being said, one subgroup that received two shots of the Pfizer or Moderna vaccines in that same cycle as opposed to two separate cycles, experienced an increase in cycle length of 2 days on average.

However, it’s believed that such effects are purely temporary and, once again, nothing to worry about.

The same team hopes to continue gathering more data spanning numerous future cycles of vaccinated women in order to confirm the suspicions that there is going to be a return to the baseline cycle length in the long run.

They also hope to expand the research on a global level in order to observe all the different effects caused by different vaccine manufacturers.


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Katherine Baldwin

Katherine is just getting her start as a journalist. She attended a technical school while still in high school where she learned a variety of skills, from photography to nutrition. Her enthusiasm for both natural and human sciences is real so she particularly enjoys covering topics on medicine and the environment.

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