Using data from research in the New England Journal of Medicine (NEJM), an article in Science, Public Health Policy, and the Law (SPHPL) claimed that over 80% of pregnant women vaccinated against Covid-19 experienced spontaneous abortions, also known as miscarriages.
This is not true.
The SPHPL article contains an error in its calculations, and the authors have told Full Fact that they are in the process of issuing a correction. We have written about misuse of this research before.
The SPHPL article and its incorrect calculation has also been reported by the Exposé, and by Health Impact News. It has also been shared on Facebook.
What does the original research say?
The original NEJM research, first published in June 2021, looked at data from the US Centers for Disease Control and Prevention’s (CDC) V-safe Pregnancy Registry, a voluntary scheme that monitors any effects of Covid-19 vaccinations on pregnancies. From among 827 “completed pregnancies” (meaning the outcome of the pregnancy was known) reported to the scheme, it found that a total of 104 ended in miscarriage, and said that this represented a miscariage rate of 12.6%, which made it similar to the normal rate in other pregnancies.
However, as the authors of the study later acknowledged, using these 827 completed pregnancies in this calculation was an error. The trouble was that 700 of the 827 participants were vaccinated towards the end of the pregnancy. Since miscarriages most often happen earlier in pregnancy, these people were less likely to experience one after their vaccinations anyway.
This meant that 700 of those pregnancies should not have been used to calculate a general risk of miscarriage after vaccination.
The NEJM article was subsequently corrected.
A new error
Looking at this research, the authors of the new article took note of the error, and used the same data to calculate a different miscarriage rate.
By their reckoning, between 114 and 127 completed pregnancies in the study were relevant, because they involved people who had been vaccinated early enough to be exposed to a significant risk of miscarriage.
They therefore expressed the same 104 miscarriages as a proportion of this much smaller total group, and said that “a re-analysis of these figures indicates a cumulative incidence of spontaneous abortion ranging from 82% (104/127) to 91% (104/114), 7–8 times higher than the original authors’ results.” Based on this, the article also called for the “immediate withdrawal” of mRNA vaccines for use in pregnancy.
But this was also an error, because most of those vaccinated early in their pregnancies had not yet reported an outcome by the time the original research was published. Miscarriages in this research are defined as spontaneous abortions before 20 weeks of gestation, whereas live births normally happen after about 40 weeks. So the first outcomes to be known, for women vaccinated early in their pregnancy, are sadly very likely to be miscarriages, whereas the outcomes not yet reported are very likely to be live births.
A similar error appeared in an article in the Exposé earlier in the year, which we fact checked before.
When we contacted the authors of the new article about this problem, they told us: “We are in the process of issuing a correction through the journal.”
What is the miscarriage risk?
Some of the authors of the original NEJM study have since followed up the remaining pregnancies where the outcome wasn’t known at the time of the original study. Using this data, they calculated a miscarriage rate in this study of around 13%, and now say that the risks of miscarriage after vaccination “are consistent with the risks of spontaneous abortion reported in the general population”.
In an article sharing this data, which has not yet been peer-reviewed, the authors say there is “no compelling biological mechanism to expect that mRNA COVID-19 vaccines present a risk to pregnancy”.
The NHS says: “There’s no evidence the COVID-19 vaccines have any effect on your chances of becoming pregnant. There’s no need to avoid getting pregnant after being vaccinated.”
Pregnancy and the Covid vaccines have been a common subject for misinformation, which we have written about before.
The Medicines and Healthcare products Regulatory Agency runs the Yellow Card scheme, where people can report any suspected side effects of the vaccines. At the time of writing, it says: “The numbers of reports of miscarriage and stillbirth are low in relation to the number of pregnant women who have received COVID-19 vaccines to date (more than 96,000 up to end of September 2021 in England and Scotland) and how commonly these events occur in the UK outside of the pandemic.
“There is no pattern from the reports to suggest that any of the COVID-19 vaccines used in the UK, or any reactions to these vaccines, increase the risk of miscarriage or stillbirth.”
The information included in this article contains the latest evidence and official guidance available at the time it was written. This is not a substitute for medical advice. If you require specific medical advice please consult your GP or midwife.