Does #CovidVaccination cause changes to #periods?

I know ppl have been wondering about this! But up to now the data we had was pretty preliminary. However, with a large, prospectively collected dataset out yesterday, I think it’s time to start putting it all together.... 🧵
Here’s some more on that new study. In short, people who received both doses of the vaccine in a single menstrual cycle found their period came a couple of days late. But it was back to normal a couple of cycles later, so the change was temporary. 2/

This might explain why our UK-based study couldn’t find clear patterns to suggest that Covid vaccination is associated with changes to periods. In the UK, our interdose interval is 8 weeks, so it’s not possible to have both doses in the same cycle. 3/

(I should say that our study was smaller with a less strong study design – so that might also explain it!) 4/
The findings from the US study are also in line with a reports from Norway, that 37.8% of ppl report a “different from usual” period in an unvaccinated cycle, compared to 39.4% after their first dose, and 40.9% after their second dose. 5/…
These differences were significant, but small. Particularly compared to the background rate at which people have “different from usual” periods. 6/
To summarise… there is some evidence of small changes to the timing and flow of periods immediately post-vaccine, and this may be mainly evident in countries such as the USA and Norway, which use a short interdose interval. The changes are also temporary. All reassuring! 7/
Finally, can we say anything about the mechanism by which these changes occur? One idea was that it might be mediated by temporary alterations to the level of sex hormones. In this case, we would expect people on hormonal contraception to be less affected. 8/
But our study actually found those on hormonal contraception more likely to report a change… 9/

A much larger survey-based study carried out by @ResourcefulSqrl and @KateClancy found the same thing… 10/…
Although, interestingly, a UK-based survey found that people using hormonal contraception *did* seem to be less likely to report a change to the period after vaccination. 11/…
The final study is somewhat less likely to be affected by reporting bias than the first two I mentioned. So I feel like the jury is still out on that one. 12/
I think we will need large, prospectively collected datasets from people on hormonal contraception to get to the bottom of this (the new US study only looked at people who were spontaneously cycling). 13/
Finally, are people who already have a diagnosis of a gynaecological or menstrual disorder more likely to notice a change to their periods? 14/
We did actually find a (weak) signal suggesting that ppl with a diagnosis of endometriosis or PCOS are more likely to report a change to the timing of their period… 15/

And the survey from @ResourcefulSqrl noted that ppl with endometriosis, menorrhagia or fibroids were more likely to report a heavier than normal period. 16/
These signals are definitely worth looking into in more detail, but in the interim, I wouldn’t say that people with these conditions should avoid the COVID vaccine... 17/
It’s important to remember that COVID infection can itself cause changes to periods, as well as the severe disease that we try to avoid by getting vaccinated! 18/18……

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More from @VikiLovesFACS

6 Jan
Does #CovidVaccination cause changes to #periods? Biggest and best study so far...

In summary: on average, periods are delayed by ~half day by dose 2 of the vaccine, and delayed by ~2 days if you get both doses in the same cycle. But it's temporary! 🧵…
3959 spontaneously cycling ppl logged at least 6 consecutive cycles with tracking app @NaturalCycles.

2403 were vaccinated. Taking them all together, the average period came 0.64d late after dose 1 and 0.79d late after dose 2. No difference in length of period. 2/
Most of us wouldn’t even notice this! But could the average be hiding some small fraction of people who experience a large change? We define any variation in cycle length of less than 8 days as “normal”. 3/…
Read 13 tweets
16 Dec 21
If you get the #CovidVaccine while you are #pregnant, what cross the placenta? 🤔

This new preprint looked at 19 people vaccinated in pregnancy, and their babies, to find out... 🧵…
👉🏻 Vaccine mRNA and Spike protein were not detectable in placenta or cord blood.

👉🏻 Anti-spike IgM was not present in cord blood (which it would be if the babies had made their own response to the vaccine).

Two previous studies also found this... 2/

👉🏻 We already know that anti-Spike IgG crosses the placenta, and might be expected to protect newborns against COVID. This study confirmed this.

This is in line with lots of previous work, which you can find under q8 of this document... 3/…
Read 5 tweets
25 Nov 21
📢 The first large scale UK data on the safety of #CovidVaccine in #pregnancy is out today from @UKHSA !

In people giving birth between January and August, 24,759 of whom were vaccinated...

🗝️ No difference in stillbirth rate between vaccinated and unvaccinated... 1/
🗝️ No difference in babies with low birthweight between vaccinated and unvaccinated... 2/
🗝️ Preterm births occurred at a rate of 6.51% in vaccinated people and 5.99% in unvaccinated people.

This small difference is likely to be because at this time vaccinated people were more likely to be older and have underlying health conditions. 3/
Read 6 tweets
19 Nov 21
When is the best time in #pregnancy to get the #CovidVaccine?


Two studies came out this week that tackle the question. And (bonus!) which vaccine to go for...

But first! I should say that all the *safety* data says that it's equally safe to get the vaccine in any trimester.

So the question here is really when it's most *protective* to get the vaccine.

Links to safety data here... 2/…
The first study, from @EdlowLab, looked at 158 people vaccinated in pregnancy, broken down by vaccine type and trimester of vaccination. 3/…
Read 15 tweets
17 Nov 21
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 21
"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/… The JCVI advises that the booster vaccine dose should be off
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/… Text from new ACOG guidance. ACOG recommends that pregnant a
But what's the evidence that #CovidVaccine #boosters are safe and effective in #pregnancy? 3/
Read 7 tweets

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