Online blogs and social media posts claim data compiled in a study concludes that over 80% of pregnancies end in miscarriage following a COVID-19 vaccine in the first or second trimester. The posts have taken figures from a table in a study published in the New England Journal of Medicine out of context.
A headline from one popular blogpost reads: “CDC manipulated study data to show the Covid-19 Vaccines are safe for Pregnant Women when in reality 4 in 5 suffered a miscarriage (archive.is/rx72Z).”
The claim was also shared on another website (archive.is/kv6ly) with a headline that reads: “BREAKING NEWS: mRNA Shots Caused Miscarriages In 82% OF Women – The REPORT DISGUISED The Facts.”
Similar claims have been made on social media, example here .
“I am pregnant and won’t ever touch the stuff! Don’t mess with me or my baby,” one person commented on Instagram.
The authors of the blog posts make a series of calculations based on table 4 within a preliminary study released in the New England Journal of Medicine (NEJM) in 2020 (here).
However, the logic is flawed, and the calculations are based on only a part of the total who took part in the study.
The preliminary report used data collected through the Centers for Disease Prevention and Control (CDC) v-safe registry which collects information from those who have received a Pfizer-BioNTech or Moderna COVID-19 vaccine while pregnant (here).
With a sample of 3,598 women who were pregnant and had also received a COVID-19 vaccine, the authors subsequently conducted a follow-up two to three months later. Initial data had been collected and a limited number of follow-ups had been made by the time the preliminary study was released.
Of the 3,958 participants, 827 had what the study defines as a ‘completed pregnancy’. This term includes those who either had a baby (what the authors call a ‘live birth’), or those who suffered from a miscarriage or still birth (termed ‘pregnancy loss’ in the study). The rest were either still pregnant or a follow-up had not yet been made by the time the preliminary analysis had been released.
Of the 827 women who had a completed pregnancy, 104 had a miscarriage. Therefore, the authors calculate that of the completed pregnancies, there was a 12.6% rate of miscarriage. (This was calculated with just those who had a completed pregnancy by the time the preliminary study had been released.)
Some of the social media posts say the rate of miscarriage should have been calculated differently. They say that miscarriage generally only occurs in the first or second trimester while a stillbirth is a loss after the 20th week of pregnancy (here) and, therefore, the rate of miscarriage should only be calculated using figures of the women who had a vaccine in the first or second trimester and not the third.
By excluding the 700 (of 827 completed pregnancies) who had the vaccine in the last trimester, the 127 remaining becomes the denominator and the rate equates to 81.9%.
This is misleading as it exempts most of the women who took part in the study, who were either still pregnant or waiting for a follow-up.
The 127 pregnancies were those that had been completed by the time the preliminary analysis had been conducted and who had their vaccine in the first or second trimester – not the total number of women who had their vaccine in the first or second trimester (1,714 and 1,019, respectively).
The outcomes of many of the pregnancies that were part of the preliminary CDC study are not yet known – as many were still pregnant.
The miscarriage rate among the total number of women in the study who had their vaccine in the first or second trimester would have been 3.8% (104 out of 2,733) – though it is worth noting the study itself was preliminary and the CDC said a new study would be released soon.
The calculations also ignore the rate of miscarriage in the general population.
“About 10-25% of known pregnancies end in miscarriage, however, the actual number is likely higher because many miscarriages occur before people are aware, they are pregnant,” the CDC spokesperson said.
“Most miscarriages occur because the fetus isn’t developing normally. About 50% of miscarriages are associated with extra or missing chromosomes. CDC experts will continue to study the effects of COVID-19 vaccination on pregnancies and closely monitor any safety concerns,” the spokesperson added.
Experts are analyzing the most recent v-safe Pregnancy Registry data and will soon publish a new report on those who were pregnant and received their COVID-19 vaccine in the first trimester, the CDC spokesperson said.
The CDC says that although there is limited data on the safety of COVID-19 vaccines during pregnancy, preliminary data has not identified any safety concerns (here).
Misleading. A study did not find that over 80% of pregnancies ended in miscarriage after COVID-19 vaccinations. Social media posts and online blogs took figures from a study out of context.
This article was produced by the Reuters Fact Check team. Read more about our fact-checking work here .
Our Standards: The Thomson Reuters Trust Principles.