How Covid-19 Vaccines May Affect Your Menstrual Cycle, Here’s What Studies Say

On February 2, Rep. Marjorie Taylor Greene (R-Georgia) tweeted: “Many women have reported problems with their menstrual cycles after taking the vaccines. And women have reported miscarriages as well. We need answers and we will be asking.” It’s not completely clear who all she meant by “we,” but maybe “we” should be looking at the peer-reviewed scientific studies that have been published to date. So far, several studies have indeed shown that you may experience a temporary lengthening of your menstrual cycle for a couple cycles after getting a Covid-19 vaccine. The long and the short of it, though, is that this lengthening was typically no more than a few days and in most cases no more than a day. And so far such temporary changes alone don’t seem likely to have longer term consequences. They also aren’t super surprising given what Covid-19 vaccines are supposed to do.

That may be quite a different picture from the picture that Taylor Greene’s “we, we” tweet seems to convey. Taylor Greene’s tweet also forwarded a Project Veritas tweet that included the following quote: “There is something irregular about their menstrual cycles…concerning…The vaccine shouldn’t be interfering with that…It has to be affecting something hormonal…” Hmm, Taylor Greene’s sharing of a Project Veritas tweet and video was, shall we say, “very interesting.” Remember, Project Veritas has been described by Ed Pilkington for The Guardian as “a discredited rightwing attack organization run by James O’Keefe that specializes in sting operations against liberal groups and the established media,” as I mentioned in a January 28 article for Forbes. That has included piecing together video clips and information without providing the proper context and background. The description “discredited rightwing attack organization” doesn’t exactly sing science. Neither does using the phrase “Medical Brown Shirts” to refer to the Covid-19 vaccination campaign or “Peach Tree Dish” to refer to, well, a Petri Dish, as Taylor Greene has. So, again, why not look at what the published peer-reviewed scientific studies have said instead?

I’ve already covered for Forbes one of these studies that was described in an April 2022 publication in the journal Obstetrics and Gynecology, This study used an app called “Natural Cycles” to follow the menstrual cycles of 2,403 women in the U.S. before and after they were vaccinated with 1,556 who did not get vaccinated. Those who had gotten their first dose of the Covid-19 vaccine had to then wait on average 0.71 days longer for their next period than they did prior to vaccination with most such increases in the 0.47 to 0.94 day range. Those who had gotten their second dose had on average a slightly greater (0.91 day) increase with most increases being somewhere from 0.63 to 1.19 days.

OK, a one day or so change in menstrual cycle length alone isn’t a sound the alarm bells situation. After all, your ovaries and uterus are not like an atomic clock. If you are using your menstrual cycle instead of a calendar to keep track of your meetings, you are going to end up missing a lot of meetings. The length of your menstrual cycle can naturally vary from cycle-to-cycle. So a one, two, or even three day difference between cycles is not something too far out of the ordinary.

Moreover, these changes tended to be quite temporary, occurring for the most part in the cycle immediately following vaccination before reverting to normal within the ensuing two cycles. Many things can cause temporary changes in menstrual cycle length, basically anything that can affect your levels of hormones like estrogen, progesterone, gonadotropin releasing hormone (GnRH), follicle stimulating hormone (FSH), and luteinizing hormone (LH). For example, intense physical activity, a bad cold, the flu, or emotional stress can perturb your menstrual cycle. So if you are breaking up with your significant other on the phone while running a triathlon when you are sick with the flu, there’s a decent chance that your menstrual cycle may be affected.

Note that the team from the Oregon Health & Science University in Portland, Oregon, (Alison Edelman, MD, MPH, Emily R. Boniface, MPH, Leo Han, MD, MPH, and Blair G. Darney, PhD, MPH), the University of Massachusetts (Kristen A. Matteson, MD, MPH), and Natural Cycles (Eleonora Benhar, PhD, Carlotta Favaro, PhD, and Jack T. Pearson, PhD) that conducted this study did not find changes in the lengths of the actual menstrual periods. In other words, while there were some increases in the time between periods, the lengths of the bleeding episodes didn’t seem to change. You could say that the study participants went with the flow that they had previously.

Several members of this research team—namely Edelman, Boniface, Benhar, Han, Matterson, Pearson, and Darney—also connected with colleagues from across the pond—Victoria Male, PhD, from Imperial College London and Sharon T Cameron, MB ChB, MD, CCST, from the University of Edinburgh in the U.K.— to conduct an even larger and a little more international version of the same study. This subsequent study, described in a September 27, 2022, publication in the British Medical Journal, included 19,622 folks from 18 to 45 years of age with 31.71% of them being from the U.K., 28.59% from the U.S. and Canada, and 33.55% from Europe. Now if you think those parts of the world represent the entire world, you haven’t head of K-pop yet.

Nonetheless, this study did encompass a relatively broader population and still found rather similar results. There was on average a 0.71 day temporary increase in menstrual cycle length after the first Covid-19 vaccine dose with most increases falling in the 0.47 to 0.96 range and a 0.56 day temporary increase after the second dose with most increases falling in the 0.28 to 0.84 range. This study did find that those who had received both vaccine doses within the same menstrual cycle tended to experience a greater lengthening, on average 3.70 days with most increases falling within the 2.98 to 4.42 day range. Once again, these changes were temporary and did not consist of any changes in the menstrual period itself.

A study in another part of the world, namely Japan, further confirmed such findings. For a study published in the Journal of Infection and Chemotherapy on January 7, 2023, Shihoko Kajiwara, Naomi Akiyama, Hisashi Baba, and Michio Ohta from the Gifu University of Health Science in Gifu-city, Japan, surveyed 280 female medical students in Japan from October 2021 to March 2022. They found that the woman experienced on average a 1.9-day lengthening of their menstrual cycles after the first dose and a 2.5-day lengthening after the second dose of the Covid-19 vaccines. This bumped up to an average 3.9-day lengthening when both doses came within a single menstrual cycle. These “lengthenings” were a bit longer than those found in the first two studies but this study also had a much smaller sample size.

Now, this Gifu University of Health Science study did find that side effects from Covid-19 vaccine such as headaches and chills were most pronounced when vaccination occurred during the menstrual period and least pronounced during the ovulation period. So getting the vaccine while you are having your period may not make you the happiest cramper so to speak.

And a study published on December 28, 2022, in the journal Influenza and Other Respiratory Viruses did find that those who had gotten vaccinated were more likely to experience worse menstrual pain and more heavy bleeding afterwards. This was based on anonymous surveys of 4,942 females from Jordan (677 participants) Syria (825), Palestine (908), Egypt (899), Libya (775), and Sudan (856) who had an average age of 24.02 years. Those who had received the Covid-19 vaccine were more likely to have had increased back pain, nausea, tiredness, pelvic pain, use of over the counter pain medications, bowel movements, and looseness of stools, although this one-time survey could not determine how many menstrual periods such symptoms lasted.

Then there was the study published in Science Advances on July 15, 2022, that consisted of a web-based survey of 39,129 people in the U.S. The team from Washington University in St. Louis (Katharine M. N. Lee, PhD, Chongliang Luo, PhD, and the University of Illinois (Eleanor J. Junkins, PhD, Urooba A. Fatima, PhD, Maria L. Cox, PhD, and Kathryn B. H. Clancy, PhD) found that after Covid-19 vaccination 42% of those folks who had regular menstrual cycles experienced heavier bleeding whereas 44% reported no change.

So how concerning should such menstrual changes be? Should you just go with the flow or are these real serious issues? Well, temporary changes in your menstrual cycle alone are not likely to significantly affect your fertility. And so far that’s been supported by data. For example, a study published in the American Journal of Epidemiology on January 20, 2022, had 2,126 females in the 21 to 45 year age range complete questionnaires every eight weeks from around when the Covid-19 vaccines became available through November 2021. The questionnaires asked various questions about the participants’ menstrual cycles, their attempts to conceive, and whether they had used fertility treatments, gotten pregnant, or suffered any pregnancy losses. There were also questions about their male partners but it wasn’t clear whether cursing was allowed for any of the responses. Ultimately, the study didn’t find any association between Covid-19 vaccination and the fertility of the females or their male partners. It did find that SARS-CoV-2 infection to be associated with a short-term decline in the fertility of their male partners. So, if you are male and got infected with the SARS-CoV-2, you may not be quite on the ball, so to speak, for a little while.

It’s not super surprising that the Covid-19 vaccines may temporarily cause relatively small changes in your menstrual cycle. After all, the vaccine is not like a fluffy pillow or mac-and-cheese or a fluffy pillow full of mac-and-cheese. It’s not purely for comfort. Instead, it’s supposed to challenge your body and cause some degree of stress temporarily. It’s a bit like how having a bad date tells you to never again swipe right on someone who says, “Doesn’t like drama” or has a list of deal-breakers that look like an apartment lease on his or her dating profile. The Covid-19 vaccines act as a controlled safer way of exposing your immune system to the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike proteins without all the get sick stuff that can come with a natural infection. This exposure prompts a reaction from your immune system, which, in turn, could potentially perturb levels of various hormones that help regulate the different steps in your menstrual cycle.

Do the studies to date completely rule out the possibility that the Covid-19 vaccine may affect your fertility? No. You can never eliminate risk by 100%. Heck, hearing the song Macarena by Los Del Rio could potentially in some way negatively affect your fertility. Your body could say, “No way,” when you get to the “Move with me, chant with me” part of the song. You shouldn’t automatically assume that something marketed by a pharmaceutical company is going to be 100% safe. That’s why independent scientists need to keep studying such products.

Ultimately, the decision to get vaccinated against Covid-19 should be based on a risk-benefit analysis. There are clearly many different risks of suffering Covid-19 including long Covid, hospitalization, and death. And death is going to affect your fertility. To date, the risks of getting Covid-19 have far outweighed the potential risks of getting the Covid-19 vaccine.

This doesn’t mean that this is a period, end of story situation. Each of the studies conducted to date has had its share of limitations. They’ve been able to show associations but not necessarily cause-and-effect. The studies haven’t observed people over longer periods of time. Therefore, rather than focus on any single study, consider what the entire body of scientific literature has been saying. Don’t “ovary-act” to any anecdotes or stories that aren’t true scientific studies either. You never know what’s behind some of those stories if they can’t be verified by a scientific peer-reveiwed study.

Therefore, researchers should continue to study the Covid-19 vaccines and their potential effects. It’s important to see if more studies done in different populations and using different approaches can confirm what has already been found about menstrual cycles and periods and fertility after Covid-19 vaccination. There are ongoing studies like the Apple Women’s Health Study, a collaboration of Harvard T.H. Chan School of Public Health, the National Institute of Environmental Health Sciences (NIEHS), and Apple that is using iPhone apps to follow the menstrual cycles for a cohort of over 100,000 participants. But other studies are needed as well. Meanwhile, Pfizer and Moderna need to be as open and transparent as possible with their clinical study data, allowing independent researchers who are not financially beholden to those companies to analyze and report on that study data themselves.

Asking for more “answers” regarding Covid-19 vaccines in general is not a bad thing. However, if politicians like Taylor Greene truly want more “answers” then shouldn’t they push for more funding to go to the National Institutes of Health (NIH) to support more scientific studies? The NIH and other non-partisan federal agencies can then offer grants for independent researchers to then further study Covid-19 vaccines. Such federal grants typically have stipulations that allow independent researchers to conduct research and come up with conclusions without any pressure from the government or anyone else. In other words, researchers can proceed from conception of the study idea to its delivery in a way that’s guided by science alone.

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