CDC Data Thus Far Show COVID-19 Vaccination Safe During Pregnancy
By Jessica McDonald
Posted on July 15, 2021
Federal vaccine monitoring systems have identified no safety concerns with the COVID-19 vaccines for pregnant people. Preliminary Centers for Disease Control and Prevention data show that miscarriage is not more frequent than expected in vaccinated people. Online posts, however, falsely contend that such data, as reported in a CDC publication, show an 82% miscarriage rate.
There is no evidence that the authorized COVID-19 vaccines pose a risk to pregnant people and their fetuses. Although pregnant people were not actively included in the clinical trials conducted prior to authorization, subsequent information about those who became pregnant during the trials and safety surveillance data following the vaccines’ rollouts thus far have indicated the immunizations are safe.
Multiple online posts, however, falsely claim that CDC data reported in a New England Journal of Medicine article published in April show that the vaccines are dangerous and trigger miscarriages.
“New England Journal of Medicine finds that women who got v4x3d – within 30 days of becoming pregnant and up to 20 weeks pregnant – had a miscarriage rate of 82%,” reads one Instagram post that garnered more than 5,000 likes in a day, using a shorthand for vaccination designed to avoid detection by fact-checkers.
A headline on Rumble, a Canadian video sharing site, also touts the false statistic, “FACT: 82% of Pregnant Women in Study Had Miscarriage.”
Two Facebook posts and an article on a dubious website similarly highlight the incorrect figure, with one claiming that the information was “deceptively buried” in a footnote in the scientific publication.
The 82% miscarriage number, which does not appear in the study, is incorrect because it is based only on people who were vaccinated in their first or second trimesters and reported completing their pregnancies in the follow-up interviews conducted by March 30. The vast majority of women who had received the vaccines that early in pregnancy could not have ended their pregnancies by the time of follow-up unless they miscarried, thereby guaranteeing a very high number from such a calculation.
“This is pure number manipulation and propaganda,” Eve C. Feinberg, an associate professor of obstetrics and gynecology at Northwestern University’s Feinberg School of Medicine, told us.
The figure also fails a basic sniff test. If 82% of pregnant people were actually miscarrying after being vaccinated, it would be very obvious that there were problems with the vaccines.
“[T]his is a ridiculous claim and simply not observed clinically,” Feinberg said.
The New England Journal of Medicine article from which the faulty percentage is derived reported on the preliminary findings of the government’s two primary vaccine safety monitoring systems — v-safe, a smartphone-based health checker run by the CDC, and the Vaccine Adverse Event Reporting System — for pregnant people who had received the Pfizer/BioNTech or Moderna vaccines. It concluded there were no “obvious safety signals among pregnant persons who received mRNA Covid-19 vaccines,” while acknowledging that additional follow-up of pregnant women, especially those vaccinated early in pregnancy, was needed.
The incorrect miscarriage calculation stems from a misinterpretation of the v-safe data, which included 3,958 people enrolled in the v-safe pregnancy registry who had been vaccinated with a first dose prior to Feb. 28. CDC researchers contacted these individuals for information about their pregnancies, and from interviews performed as of March 30, 827 people had completed them, either through birth, pregnancy loss or induced abortion. Of these completed pregnancies, 104, or 12.6%, had experienced a “spontaneous abortion,” also known as a miscarriage, before 20 weeks.
It’s this percentage that the CDC authors reported in table 4. According to the published literature — also cited in the table — 10-26% of pregnancies end in miscarriage, so 12.6% is within the normally expected range.
Online posts, however, have latched onto a footnote in table 4 that says 700 of the 827 participants “received their first eligible dose in the third trimester.” Because these participants couldn’t have miscarried before 20 weeks, the posts argue, the 700 people should be subtracted from the 827, making the calculation 104 miscarriages out of 127 pregnancies, or 82%.
Experts, however, say that doing the math that way is incorrect.
“[T]he quoted rate of [82%] is not the miscarriage rate,” Viki Male, a lecturer in reproductive immunology at Imperial College London, said on Twitter. “It just tells us that we can’t go from the first trimester to giving birth to a healthy baby in three months.”
“[T]his is a bit of a meaningless statistic, since the only way you can complete your pregnancy within 3 months, starting in the first trimester, is to miscarry,” she added. “And presumably the only reason that rate isn’t 100% is because some people vaccinated at the end of the 2nd trimester completed their pregnancies within 3 months by giving birth.”
In a statement to FactCheck.org, the CDC also said such percentages are erroneous. “This is not an appropriate calculation based on the data available because more than a 1000 pregnancies were ongoing and outcome data was not available at the time of the report,” the agency said, adding that it “will continue to study the effects of COVID-19 vaccination on pregnancies and closely monitor any safety concerns.”
Other data provided in the paper allow for a different calculation that avoids the problem of including participants who were vaccinated after 20 weeks, although it has limitations.
“[T]he real way to calculate this is to look at all patients who received the vaccine, not just the patients who completed pregnancy,” Northwestern’s Feinberg said.
Data in the paper show that a total of 1,224 people were vaccinated around the time of conception or in the first trimester, so 104 miscarriages out of this total is a miscarriage frequency of 8.5%, she said. And correctly limiting it to just the 96 participants who had a first trimester loss to match the denominator drops the percentage to 7.8%.
Feinberg said she didn’t know why the CDC didn’t report this frequency instead. Martha Sharan, a CDC spokesperson, told FactCheck.org that doing the calculation as suggested by Feinberg makes some sense, but would be an underestimate because it’s not known for certain that all the other women didn’t miscarry.
“We don’t know what happened to them. We only know what happened to the 827. That’s why they decided to use the 827, because there were definite outcomes,” she said, adding that the research team would be publishing a new report with longer follow-up soon.
In an email to the fact-checking site Lead Stories, Sharan explained that the agency struggled with how to best report the data, given that so many participants were still pregnant or had not yet reported an outcome to the registry.
“We felt it was important to report all spontaneous abortions that had been observed in the registry thus far. At the same time, we also wanted to limit the analysis to pregnancies for which [we] had final outcome data as there may be completed pregnancies we are not yet aware of because they have not had a scheduled follow-up call,” she said.
“In a future report in which more follow-up time has passed, we plan to limit the assessment of spontaneous abortions to completed pregnancies vaccinated at less than 20 weeks and whose estimated date of delivery has passed,” Sharan added. “Because of where we were in the vaccination efforts at the time of data analysis, that method provided both a numerator and denominator of zero. We therefore chose to report spontaneous abortions among all completed pregnancies in this preliminary report.”
In her Twitter thread, Male said that both the CDC method and the way Feinberg recommended for calculating the proportion of miscarriages are imperfect. “[G]iven this, I can see why the authors went with reporting the conservative (ie. higher) rate,” she said. “But no matter how we calculate it, it’s still not more than that normal rate.”
The New England Journal of Medicine article was upfront about the fact that the data on miscarriage were limited. “Whereas some pregnancies with vaccination in the first and early second trimester have been completed, the majority are ongoing, and a direct comparison of outcomes on the basis of timing of vaccination is needed to define the proportion of spontaneous abortions in this cohort,” the paper reads.
“[A]s more patients deliver, the true denominator will become apparent,” Feinberg said. “The data will speak for itself, vaccination is safe in pregnant patients.”
As we’ve written before, in contrast to evidence that COVID-19 can increase pregnancy complications, there is no evidence that COVID-19 vaccines are dangerous to pregnant people.
Even though pregnant people were excluded from the vaccine clinical trials, some individuals did become pregnant while participating — and those receiving the immunizations did not miscarry more frequently. Moreover, reproductive toxicity studies of the vaccines in pregnant animals revealed no safety concerns, and as the American College of Obstetricians and Gynecologists has pointed out, based on how the vaccines work, there is no reason to think they would be any less safe for pregnant people compared to those who are not.
A report published in the journal F&S on June 2 also found no difference, based on vaccination status, in the ability of an embryo to implant or to remain viable in early pregnancy among women who were undergoing in vitro fertilization to become pregnant. The results further support the idea that the vaccines are safe for pregnant people and do not have harmful effects on fertility, an unsubstantiated claim we have previously addressed.
Similarly, a paper published in the Journal of the American Medical Association on July 12 found that immunization with the Pfizer/BioNTech vaccine in Israel was associated with protection against infection with the coronavirus among pregnant women, with no difference in the frequency of induced or spontaneous abortions or other negative birth outcomes in those who were vaccinated compared to matched unvaccinated controls.
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 our 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.
Spencer, Saranac Hale. “Evidence Points to Safety of COVID-19 Vaccines for Pregnant People.” FactCheck.org. 11 Jun 2021.
Feinberg, Eve C. Associate professor of obstetrics and gynecology, Northwestern University Feinberg School of Medicine. Emails to FactCheck.org. 10 and 12 Jul 2021.
Shimabukuro, Tom T. et al. “Preliminary Findings of mRNA Covid-19 Vaccine Safety in Pregnant Persons.” The New England Journal of Medicine. 21 Apr 2021.
“V-safe After Vaccination Health Checker.” CDC. Accessed 14 Jul 2021.
Male, Viki (@VikiLovesFACS). “This @NEJM paper on the safety of #COVID19 #vaccines during #pregnancy found no increased risk of miscarriage associated with vaccination. So why is this person claiming that there was an 83% rate of miscarriage? Short answer, a maths mistake…” Twitter thread. 1 Jul 2021.
Tereszcuk, Alexis. “Fact Check: New England Journal of Medicine Did NOT Find 82% Miscarriage Rate Among Pregnant Women Vaccinated Against COVID-19.” Lead Stories. 10 Jul 2021.
Sharan, Martha. CDC spokesperson. Phone interview with FactCheck.org. 13 Jul 2021.
CDC statement on COVID-19 vaccination and miscarriage. Email to FactCheck.org. 14 Jul 2021.
Quenby, Siobhan et al. “Miscarriage matters: the epidemiological, physical, psychological, and economic costs of early pregnancy loss.” Lancet. 1 May 2021.
“COVID-19 Vaccines and Pregnancy: Conversation Guide for Clinicians.” The American College of Obstetricians and Gynecologists. Accessed 14 Jul 2021.
Morris, Randy. “SARS-CoV-2 spike protein seropositivity from vaccination or infection does not cause sterility.” F&S Reports. 2 Jun 2021.
“New Study Reveals Covid Vaccine Does Not Cause Female Sterility.” American Society for Reproductive Medicine press release. 24 Jun 2021.
Goldshtein, Inbal et al. “Association Between BNT162b2 Vaccination and Incidence of SARS-CoV-2 Infection in Pregnant Women.” JAMA. 12 Jul 2021.
Male, Viki (@VikiLovesFACS). ““This study took 7530 #pregnant ppl who had received 2 doses of Pfizer #COVID19 #vaccine and compared them to 7530 matched unvaccinated ppl…” Twitter thread. 13 Jul 2021.