Studies have repeatedly found that COVID-19 vaccination does not increase the risk of miscarriage. Bogus claims that 44% of pregnant women in the Pfizer/BioNTech COVID-19 vaccine trial miscarried rely on a faulty tally of miscarriages that counted each miscarriage twice and included miscarriages from people in the placebo group.
Numerous studies have found that COVID-19 vaccination is safe during pregnancy and doesn’t raise the risk of miscarriage.
Results from the Pfizer/BioNTech clinical trial are consistent with those findings, with just three spontaneous abortions, or miscarriages, reported among 50 participants who became pregnant and received the vaccine at some point during the trial. The miscarriage rate in the trial was normal and isn’t more than what was observed in placebo recipients.
And yet, social media has been abuzz with the false claim that during Pfizer’s main clinical trial, 44% of the pregnant women who were vaccinated miscarried.
“Massacre: Nearly Half of Pregnant Women in Pfizer Trial Miscarried,” reads an incorrect headline from an Aug. 16 story from the conservative website the Florida Standard. A screenshot of the article was shared on Instagram and received more than 12,000 likes in two days.
Origin of the False 44% Statistic
The claim originates from a post on the Daily Clout, a website run by Naomi Wolf, an author and former Democratic consultant who has trafficked in conspiracy theories for years.
Estimates vary, but miscarriage, or pregnancy loss before 20 weeks, is common and occurs in some 10% to 20% of known pregnancies.
Based on a document Pfizer submitted to the Food and Drug Administration that was made public through a Freedom of Information Act request, the post contended that it found 22 instances of miscarriage out of the 50 subjects who reported pregnancy after dose one — hence the 44%.
But the tally is incorrect. There are only 11 unique miscarriages listed in the Pfizer document. Each miscarriage was counted twice because they appear in two tables: one for all adverse events for all subjects (listing 188.8.131.52.1) and one for just the serious adverse events for all subjects (listing 184.108.40.206). Furthermore, as the table names suggest, those are the miscarriages reported for all subjects — vaccine and placebo recipients combined.
When cross-checking the subjects with a document that shows whether a participant was assigned to the placebo or vaccine group, FactCheck.org found that three of the 11 miscarriages were among vaccine recipients. The remaining eight miscarriages were in the placebo group, which also reported one induced abortion.
As a result, the 44% statistic is completely spurious.
And indeed, only three of the miscarriages appear in the document’s list of the 50 subjects reporting pregnancy after dose one (listing 220.127.116.11). According to the listing, 42 of the subjects were assigned to the vaccine group, while eight were originally assigned to the placebo group but chose to be vaccinated after unblinding. After the FDA authorized the Pfizer/BioNTech vaccine, trial participants were told whether they had received the vaccine or the placebo, meaning the trial was unblinded.
This data align well with the FDA’s review of the trial’s pregnancy data, which lists three spontaneous abortions out of 42 pregnancies in the vaccine group compared with seven spontaneous abortions out of 47 pregnancies in the placebo group (table 35). There were no spontaneous abortions in the eight subjects reporting pregnancy who were vaccinated after unblinding (table 36).
“The known pregnancy outcomes of spontaneous abortion, miscarriages and elective abortions was similar between the vaccine and the placebo group,” the FDA review notes.
In other words, there is nothing to indicate from the trial that vaccination was dangerous to pregnant individuals and increased the risk of miscarriage.
By Aug. 17, the Daily Clout post had added a correction of sorts, noting that other people online had identified a different number of miscarriages from the Pfizer document. But other outlets were already circulating the story, and Naomi Wolf herself had appeared on Steve Bannon’s podcast “War Room” two days earlier to promote the claim.
“Over a year ago, the FDA received this report that out of 50 pregnant women, 22 of them lost their babies,” she said in her Aug. 15 appearance on Bannon’s show, before linking the inaccurate findings to a supposed “baby die-off” (see the video at about 21:20 minutes in).
There is no evidence of any such “die-off.” Here, as before, Wolf pointed to supposed data from Scotland, Ontario and Israel — but as we and other fact-checkers have written, those claims are groundless.
Wolf also complained that Twitter had already blocked Daily Clout’s Twitter account for trying to share the 44% statistic. She asserted that it was impossible for the miscarriage claim to be false.
“When they call this misinformation, my post-Enlightenment head wants to explode,” she said (see the video at about 16 minutes in). “This is primary source documentation — it doesn’t get better than that. This is an internal set of documents released under court order; these are Pfizer’s own documents, right? And they’re analyzed by the most highly credentialed people, and the links are right there. So there is literally no way … this can be misinformation.”
Wolf, who is a frequent guest on Bannon’s show and sometimes referred to as “Dr.,” has no background in science; her doctorate is in English literature. She was suspended from Twitter in June 2021 for COVID-19 vaccine misinformation.
Pregnancy and COVID-19 Vaccination
Despite the fearmongering on social media, more and more evidence suggests COVID-19 vaccination is not only safe during pregnancy, but protective to both the mother and the fetus.
The Centers for Disease Control and Prevention and the American College of Obstetricians and Gynecologists recommend that pregnant individuals get vaccinated.
Initially, it wasn’t known very well whether the vaccine would be safe during pregnancy, although there was no biological reason to think that it would be harmful. That’s because, like most clinical trials, the vaccine trials excluded pregnant participants. Despite the exclusions, a small number of people still got pregnant, which is why there is a limited amount of data from the trials.
In response to the 44% miscarriage claim, Victoria Male, a lecturer in reproductive immunology at Imperial College London, noted on Twitter that the miscarriage rate for people who became pregnant during the Pfizer trial was 7% for the vaccine group and 15% for the control group.
“These rates are not significantly different from each other, or from normal,” she said.
Trials for other vaccines showed similar results.
“Because trial participants were asked not to become pregnant, the trial data – although reassuring – is not from many pregnancies. We can get a better idea of COVID vaccine safety in pregnancy by looking at the bigger and better datasets generated independently by government bodies and universities,” Male told us in an email.
Male has been tracking the many studies — and told us that of the eight studies looking at miscarriage, which include nearly 72,000 people who were vaccinated during pregnancy, none found “any increased rate of miscarriage associated with vaccination.”
And as she’s detailed in her continually updated explainer on COVID-19 vaccination and fertility, pregnancy and breastfeeding, a total of 27 studies tracking various outcomes after pregnancy have not found an increased risk of other bad outcomes following COVID-19 vaccination, either — including preterm birth, stillbirth or babies being born smaller than expected, or with congenital abnormalities.
“A meta-analysis taking in many of these studies, published in May 2022, found that COVID vaccination actually reduces the rate of stillbirth by 15%, presumably because it prevents stillbirths that occur because of COVID infection,” she added in her explainer.
Wolf’s specific claim is not only incorrect, but the entire premise that vaccination is harmful to pregnant people is contradicted by the available evidence.
Editor’s note: SciCheck’s COVID-19/Vaccination Project is made possible by a grant from the Robert Wood Johnson Foundation. The foundation has no control over FactCheck.org’s editorial decisions, and the views expressed in our articles do not necessarily reflect the views of the foundation. The goal of the project is to increase exposure to accurate information about COVID-19 and vaccines, while decreasing the impact of misinformation.
Male, Viki. “COVID-19 vaccine safety in pregnancy – table of studies.” Updated 23 Aug 2022.
Fisher, Max. “The insane conspiracy theories of Naomi Wolf.” Vox. 5 Oct 2014.
“Miscarriage.” Mayo Clinic. Accessed 24 Aug 2022.
Listing of Adverse Events. Pfizer document made available in FDA FOIA. Accessible from Public Health and Medical Professionals for Transparency.
“Listing of Randomization Scheme and Actual Vaccine Received.” Pfizer document made available in FDA FOIA. Accessible from Public Health and Medical Professionals for Transparency.
Wollersheim, Susan and Ann Schwartz. Clinical Review Memo for Comirnaty. FDA. 23 Aug 2021.
Jones, Brea. “Doctor Makes False Claim About Stillbirths in Canadian Hospitals.” FactCheck.org. 16 Dec 2021.
“US author Naomi Wolf falsely claims Covid-19 vaccinated mothers caused ‘baby die-off.’” AFP Malaysia. 27 Jun 2022.
“Covid: Twitter suspends Naomi Wolf after tweeting anti-vaccine misinformation.” BBC. 6 Jun 2021.
“COVID-19 Vaccines While Pregnant or Breastfeeding.” CDC. Updated 14 Jul 2022.
“COVID-19 Vaccination Considerations for Obstetric–Gynecologic Care.” ACOG. Updated 5 Aug 2022.
Male, Viki (@VikiLovesFACS). “For those interested in the miscarriage rate among those who became pregnant during the trial of the Pfizer #CovidVaccine….” Twitter. 18 Aug 2022.
Spencer, Saranac Hale. “Evidence Points to Safety of COVID-19 Vaccines for Pregnant People.” FactCheck.org. 11 Jun 2021.
Jaramillo, Catalina. “No Evidence Vaccines Impact Fertility.” FactCheck.org. 26 Feb 2021.
McDonald, Jessica. “CDC Data Thus Far Show COVID-19 Vaccination Safe During Pregnancy.” FactCheck.org. 15 Jul 2021.
Male, Viki. Lecturer in Reproductive Immunology at Imperial College London. Email to FactCheck.org. 24 Aug 2022.
Male, Viki. “Explainer on COVID vaccination, fertility, pregnancy and breastfeeding.” Updated 23 Aug 2022.