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Debunked: No, 82% of women vaccinated against Covid-19 in the first third of pregnancy don't miscarry

The claim has circulated widely on social media in recent weeks.

For debunks

A NUMBER OF claims which have been widely shared on social media have linked Covid-19 vaccines to a high number of miscarriages.

They suggest that women who receive a Covid-19 vaccine in the first trimester of their pregnancy are at high risk of experiencing a pregnancy loss.

Claimants often cite a statistic that 82% of women who got vaccinated with an mRNA vaccine experienced a pregnancy loss – although there are variations on that percentage and the stage at which a woman was vaccinated.

These claims are untrue: vaccinating pregnant women against Covid-19 does not lead to significantly higher rates of miscarriage.

The 82% figure appears to derive from claims made about data contained within a study published in June.

A number of claimants have cited this study when suggesting that the miscarriage rate among women who have been vaccinated against Covid-19 during the first trimester is 82%.

But the research that was published in that journal does not say this.

What the research actually found was that just 12.6% of the women involved in the study whose pregnancies had ended by the time of publication had experienced a miscarriage.

This is in line with the average rate in the US (where the study was carried out), as well as the rate cited by researchers in Ireland and in the UK.

The study concluded that there were “no obvious” safety issues among pregnant women who received mRNA vaccines at the time of publication, although the researchers did acknowledge that data was limited and that further research was required.

The 82% figure is incorrect, because claimants have cherry-picked data that does not account for all pregnancies involved in the study.

In reality, many of those pregnancies are still ongoing or researchers have not heard back from the women involved. The vast majority of pregnancies that were completed by the time the study was published also ended in a live birth.

The study

The 82% claims are based on a study published on 17 June in the New England Journal of Medicine titled ‘Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons’.

The authors looked at the pregnancy outcomes of almost 4,000 women who were given a dose of an mRNA vaccine against Covid-19 between 14 December 2020 and 28 February 2021.

The researchers contacted 3,958 pregnant women who were vaccinated against Covid-19 and looked at how many of them had pregnancies that resulted in live births, miscarriages, pre-term births, congenital anomalies, and neonatal deaths.

At the time of publication, 827 women had finished their pregnancy. 712 of these had given birth to healthy babies and 104 had experienced a miscarriage; the remainder had induced abortions or ectopic pregnancies, and there was one stillbirth.

The remaining women – over 3,100 people – were still pregnant or had not followed-up with the study’s authors by the time the research was published.

The researchers therefore concluded that 12.6% of women had experienced a miscarriage, which they worked out by calculating the total number of miscarriages (104) as a proportion of  the total number of completed pregnancies (827).

Again, these 827 cases referred only to the number of women whose pregnancies were completed at the time the research was published.

Counting differently

But claimants who point to the 82% figure have wrongly suggested that the rate of miscarriage should be counted differently.

They point to the fact that 700 of the 827 women who completed their pregnancy were vaccinated against Covid-19 during the third trimester, when miscarriage is less likely to occur because fetuses are more developed.

One Irish doctor recently tweeted that the miscarriage rate is 82% for women vaccinated in the first trimester only.

This statistic lines up with claims about this study (although the same doctor cited the VAERS system, which doesn’t appear to show this and which The Journal previously debunked vaccine claims, when asked for the source of his data).

This is a flawed use of statistics, because it selectively removes of 700 women from the data – all of whom happened to have live births after being vaccinated – for the only reason that they were in the third trimester when they were vaccinated.

Those 700 pregnancies were still complete pregnancies in women who had received an mRNA vaccine – one cannot simply remove them because they did not miscarry.

There is nothing in the research that says women who were vaccinated in the first and second trimesters were more susceptible to miscarriages than those vaccinated in the third trimester.

And the remaining 127 women were not just vaccinated in the first trimester: some were also vaccinated in the second trimester.

Crucially, those 127 pregnancies were only those which had been completed by the time the study was published.

That does not mean they were the only women vaccinated at that stage: an additional 3,000 pregnancies – involving a large number of women who were vaccinated at the same time as those who miscarried – were not recorded as complete in the study.

We do not actually know the pregnancy outcomes of many women who were vaccinated in the first trimester, because they have not given birth yet.

So it is not reasonable to deduce the effects of vaccination on women who got an mRNA vaccine in early pregnancy based on 127 outcomes alone.

Doing this assumes that these 127 women were the only people involved in the study who were vaccinated in the first and second trimester, when this is not the case.

‘Meaningless’ data

Yet this selective number is where the 82% statistic comes from.

Removing 700 pregnancies (women who were vaccinated in the third trimester) from the total number of completed pregnancies in the study (827) leaves 127 completed pregnancies – specifically, in women who were vaccinated in the first or second trimester.

This methodology allows one to calculate a miscarriage rate of 82% based on the total number of miscarriages (104) as a proportion of the total number of completed first- and second-trimester pregnancies (127).

Yet the 127 first and second-trimester pregnancies that were completed are more likely to have ended in miscarriages regardless – that is why the were completed so early.

Victoria Male, a professor in reproductive immunology at Imperial College in London and who described the 82% statistic as “meaningless”, explained why.

“We can’t go from the first trimester to giving birth to a healthy baby in three months [when researchers followed up with women involved in the study],” she said. 

When the paper was published, the researchers involved acknowledged that the study was ongoing and that more data was needed to deduce final outcomes.

Many women involved were still pregnant at the time of publication, and the research has yet to be updated to include their birth outcomes.

But at no point did the researchers link the rate of miscarriage to the stage of pregnancy at which a woman was vaccinated.

Only 12.6% of women who had completed their pregnancies by the time the study was published had experienced a miscarriage – a proportion that is in line with usual rates.

It is false to say that 82% of pregnant women who are vaccinated against Covid-19 later experience a miscarriage.

The Journal’s FactCheck is a signatory to the International Fact-Checking Network’s Code of Principles. You can read it here. For information on how FactCheck works, what the verdicts mean, and how you can take part, check out our Reader’s Guide here. You can read about the team of editors and reporters who work on the factchecks here

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