Wondering if #COVID19 #vaccination affects #periods? 💉🩸🤔

So was I!

Preliminary results from my study on this are out today in preprint... 🧵

To answer this question, we recruited two cohorts.

Cohort 1 consists of 250 people recruited before they received their COVID vaccine, who are keeping a record of their periods before and after vaccination. 2/
This cohort will give us an idea of how common it is to experience a menstrual change after COVID vaccination.

But many of them are still tracking their cycles, so we still have to wait for all the data to come in! 3/
Cohort 2 consists of 1273 people recruited *after* they received their vaccine. These people already had their own records of their periods, and of when they received the vaccine. We asked them to use these records to tell us about their experiences. 4/
We can't use this cohort to tell us how common menstrual changes after vaccination are: we think that it will be enriched for people who experienced a change and want to talk about it! 5/
But we *can* use it to look for patterns that we would expect to see if there was a biological link between vaccination and menstrual cycle changes.

So what did we see? 6/
First, the brand of vaccine you receive makes no difference to how likely you are to report a change to your next period. So if there is a link, it is likely to be due to immune activation, rather than any specific vaccine ingredient. 7/
A potential link could be mediated by immune effects on the hormones that drive the menstrual cycle. If this is the case, we would expect that people on hormonal contraception would be less likely to experience a change than those naturally cycling.

But we didn't see this... 8/
We could hypothesise that vaccination in the first half of the cycle might delay or prevent ovulation, lengthening the cycle. Then, we would expect to see a change to cycle length mainly in those vaccinated in the first half of the menstrual cycle.

But we didn't see this... 9/
So in this cohort, we did not detect a strong signal consistent with COVID-19 vaccination causing menstrual changes in most people. 10/
However, we did find that people with endometriosis were slightly more likely to have an early period, and people with PCOS more likely to have a late one. This should be investigated further, but in the interim... 11/
If you have endometriosis or PCOS, I would still recommend getting vaccinated! Remember that COVID itself can mess with your cycle. 12/


This isn't a very strong signal, but it could potentially suggest that there is a subgroup of people that might be vulnerable to menstrual changes following COVID vaccination. 13/
It's also important to remember that this was a UK-based study. Different vaccines, or vaccine schedules, used elsewhere might produce different results. 14/
Finally, there are bigger and better-powered studies out there! I did this one because I was frustrated that no-one else seemed to be doing anything. But the bigger ones may be able to detect small or uncommon changes that we could not here. 15/

When those report, you can be sure I'll be talking about it. But in the meantime, from these 1273 people...

🩸 No strong signals to support the idea that #COVID19 #vaccination is linked to changes in #periods in most people.


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More from @VikiLovesFACS

17 Nov
How can we know that #COVID19 #vaccines will not harm #fertility? Could an effect unexpectedly appear years into the future?


Let’s start with the data we have on fertility right now.

👉🏻 No reduction in pregnancy rates in vaccinated (vs unvaccinated) ppl in clinical trials.

👉🏻 Egg quality, fertilisation rates and pregnancy rates are the same in vaccinated and unvaccinated IVF patients. 2/
👉🏻 No difference in sperm quality before vs after vaccination. 3/
Read 13 tweets
17 Nov
"I'm #pregnant, and I've been offered a #CovidVaccine #booster. Should I accept?"

@RCObsGyn encourage all pregnant ppl in the UK to get their booster when they are offered it... 1/

rcog.org.uk/en/guidelines-… The JCVI advises that the b...
If you are in the USA and pregnant or recently pregnant, you will be offered a booster vaccine as soon as you are six months out from dose 2. And @acog recommends you get it. 2/

acog.org/clinical/clini… Text from new ACOG guidance...
But what's the evidence that #CovidVaccine #boosters are safe and effective in #pregnancy? 3/
Read 7 tweets
3 Nov
A bunch of people have been in touch about this paper. Has a review of the evidence really raised questions about the safety of the Pfizer #COVID19 #vaccine in #pregnancy?

TLDR: No… 🧵
The paper purports to present a reanalysis of the V-safe pregnancy registry data to the end of February. You can find the original report (which concluded no increased risk of pregnancy complications following vaccination) here… 2/

But before we get into the details of what’s been done here…

There is no need to scry the six-month-old data from Shimabukuro! It was difficult to interpret because of the limited follow-up time, but *luckily* we now have longer follow-up data… 3/

Read 10 tweets
21 Oct
Stressful times (war, famine) are associated with people experiencing more anovulatory and abnormal menstrual cycles.

But what about the pandemic? This paper used data from 18,076 ppl tracking their cycles with @NaturalCycles app to investigate… 🧵

The authors looked at user data entered from March - September 2019 (pre-pandemic) compared to March - September 2020 (Pandemic). They also asked users to rate their stress levels (retrospectively) in the pre-pandemic and pandemic periods. 2/
The average cycle length decreased from 29.4 to 29.q6 days, and the average period of menstruation increased from 4.21 to 4.23 days.

Neither of these changes is clinically significant. 3/
Read 13 tweets
17 Oct
Are you #breastfeeding? Thinking about whether to get the #COVID19 #vaccine?


This is a thread for you!

People who are breastfeeding can sometimes get forgotten in the focus on pregnancy. But your questions matter too! And I particularly want to make space to address those questions because a lot of people have contacted me, worried about one particular blog post... 2/
I'll get to that later. But let's start by saying that @RCObsGyn and @MidwivesRCM recommend the COVID vaccine if you are breastfeeding. 3/

Read 18 tweets
14 Oct
Wondering if antibodies raised against #COVID19 #vaccines can bind to the placental protein syncytin-1 and harm #fertility?


Out yesterday! More data that addresses this question!

Spoiler alert: they don’t... 🧵

But why would anyone even think that such a thing might happen? Is it even worth researching?

The rumours that COVID19 vaccines would impact fertility were started by a vaccine skeptic who proposed that this might occur, so this is something that a lot of ppl may have heard. 2/
People who work in this area never thought this was very likely, for a number of reasons.

Not least, if this did happen COVID 🦠 would be associated with infertility or problems in early pregnancy, and luckily we don’t see that. 3/

Read 7 tweets

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