Thread by @VikiLovesFACS

This @NEJM paper did long-term follow-up on 3958 #pregnant ppl who received a #COVID19 #vaccine.

👉🏻 No increased risk of pregnancy-specific adverse events (including #miscarriage).

So why are ppl claiming it shows a 24x increased risk of miscarriage? 🧵

10.1056/NEJMoa2104983

The rate of miscarriages reported in the paper is 12.6%.

But is that higher than we would normally see?

No... 2/

The normal range quoted in the paper, based on these references, is 10 - 26%.

The range is large because lots of things affect miscarriage rate, so it varies a lot between studies.

But note the rate in the vaccinated population is within this normal range. 3/

If we want a tighter estimate of miscarriage rates in the general population, the best one (in my opinion) is from this recent review in @TheLancet - 15.3%.

Compared to 12.6% in the COVID vaccine safety study. 4/

thelancet.com/journals/lance…

Some people might be surprised that the miscarriage rate is as high as that. We perhaps have an artificially low view of how common miscarriage is because we tend not to talk about it.

But that’s a conversation for another time. Back to the paper... 5/

So the paper shows no increase in miscarriages following vaccination.

(Or preterm birth, or stillbirth.) 6/

So where does this claim of a 24-fold increase in miscarriages come from? 7/

Okay, let’s take a look at that dataset from the CDC, that it is claimed shows the rate of miscarriage at only 0.59%... 8/

cdc.gov/nchs/data/nvsr…

The paper is actually about *stillbirths* (fetal loss after 20 weeks), rather than miscarriage, which occurs before 20 weeks. 9/

So that 24-fold figure comes from comparing miscarriages (loss before 20 weeks) with stillbirth (loss after 20 weeks). But we know that miscarriage is much more common than stillbirth, so this is what we would expect for such a comparison. 10/

If we compare miscarriages in the vaccinated population with miscarriages in the general (unvaccinated) population, the rates are the same.

That is to say, there is no increased risk of #miscarriage associated with #COVID19 #vaccination. 11/

I hope this clears up where this idea has come from, as well as setting out the actual rates.

As always, happy to talk to ppl who feel like they need more info in order to make their decision on this. 12/12

PS. I managed to give the DOI for the NEJM paper we are discussing, rather than the link. Oops! Here’s the link...

nejm.org/doi/full/10.10…