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How the COVID-19 vaccine affects your menstrual cycle

AYESHA RASCOE, HOST:

Some people have said that they noticed changes in their menstrual cycle after getting the COVID-19 vaccine, and there has been some concern over what that could mean. But a new study published in the British Medical Journal last week has some answers. It looked at period-tracking data and did find that the COVID vaccine could affect menstrual cycle length - that is from the first day of a period through the start of the next period. Dr. Alison Edelman is a professor of obstetrics and gynecology at Oregon Health & Science University. She's also the lead researcher on the newest study, and she joins us now. Welcome to the program.

ALISON EDELMAN: Thanks, Ayesha. Pleasure to be here.

RASCOE: So this new study is building off a previous one published earlier this year, which only looked at people in the U.S. What did that study find?

EDELMAN: So that study found pretty much the same thing that we're finding in this study as well, which is that the cycle length was slightly longer - about a day - and that we weren't able, at the time, to see if it returned back to normal or when it returned back to normal.

RASCOE: OK, and so did you get more expansive data in this latest study?

EDELMAN: We really wanted to see - because this is impacting everybody globally - is our data from the U.S. comparable to the data globally with different vaccines? And then we also wanted to see what happens post-vaccine.

RASCOE: So what did you find in this new study, you know, when you take into account, like, what happened post-vaccine, et cetera?

EDELMAN: Yeah, so this study really confirms the findings that we had in the U.S. cohort. We're seeing that less-than-one-day change with getting a vaccine if you get one vaccine in the cycle. And then the cycle post-vaccine - that clean vaccine - post-vaccine cycle - we're seeing the cycle get back to normal. And our study also looked at the days of bleeding that individuals have, and we didn't see an impact of COVID vaccine on the number of days of bleeding.

RASCOE: OK. So is this kind of extended-cycle menstruation cycle - is that harmful? Is that something to be concerned about?

EDELMAN: So normally, no. But what happened at the beginning of the vaccine rollout is we just didn't have any information at all, and people were having this experience. And then we didn't have any information to give them. So they - you know, we were getting a lot of the public reporting pushback that, you know, their providers were saying this couldn't be possible, this isn't happening. And they were reporting that it did happen. And so it's information that we didn't have before around vaccines, and so we're pleased to be able to have that information now, so that people can know what to expect.

RASCOE: So clinically, one day is not significant. It's not harmful. But it could, you know, impact a person personally, right? I mean, obviously, a period is very intimate.

EDELMAN: Yeah. You know, half the population has a relationship with their menstrual period. And so we have a personal narrative, and it means something different to us. For one day difference, it could be a big deal to some individuals, personally. And so I want to make sure that we're validating what people are experiencing. When we have absence of evidence, I think, in particular for women, girls and individuals who menstruate, oftentimes our concerns get downplayed.

RASCOE: And I know that this study did not look at necessarily, like, why this happened, but can you talk about - or do you - is there any sense or any guess that you might have for why this happened? And I bring this up only because, around vaccines, there's been a lot of talk about people being concerned about it affecting fertility, et cetera.

EDELMAN: That's a great question. You know, because menstrual cycles really mean a lot to individuals. They mean that people are metabolically normal, healthy and then they also give us a look into future for fertility. And so I want to reassure people that, really, we are not seeing a signal that's harmful. But we're seeing something that people want to know about. They want to know what to expect, what to experience.

RASCOE: People on hormonal contraceptives were not included in these studies. Can you tell us about, like, how the cohorts were selected?

EDELMAN: Yeah. So these populations - you know, when we go back, we don't know, really, anything about menstrual cycles and vaccines. And so we needed to look at, is this happening? Because we know menstrual cycles have fluctuations anyway. And so is the fluctuation happening? Is that true and unrelated to the vaccine, or is it happening because of the vaccine? And because of that, we needed individuals that were having normal, natural cycles - so without hormones - to be able to see if the signal is there and if it can be connected with the vaccine. And we looked at individuals who were vaccinated and then also reported unvaccination (ph), so we had a control group to be able to compare, whereas hormonal contraception, you know, kind of overrides the signaling for menstrual cycles. And so now that we know that we have this change - or this influence from the COVID-19 vaccine, now we can apply this to other groups.

RASCOE: Dr. Alison Edelman is a professor of obstetrics and gynecology at Oregon Health & Science University. Thank you so much for joining us.

EDELMAN: Oh, thanks so much. It's been a pleasure. Transcript provided by NPR, Copyright NPR.

Ayesha Rascoe is a White House correspondent for NPR. She is currently covering her third presidential administration. Rascoe's White House coverage has included a number of high profile foreign trips, including President Trump's 2019 summit with North Korean leader Kim Jong Un in Hanoi, Vietnam, and President Obama's final NATO summit in Warsaw, Poland in 2016. As a part of the White House team, she's also a regular on the NPR Politics Podcast.