No, COVID-19 vaccines don’t increase miscarriage rates

U.S. Sen. Ron Johnson, a Wisconsin Republican, has revived a years-old inaccurate theory that COVID-19 vaccines are linked to higher rates of miscarriages.

As part of a Senate investigation into former U.S. infectious diseases chief Dr. Anthony Fauci, Johnson pointed to publicly released text messages Fauci exchanged with two of former President Joe Biden’s top health officials. In them, Fauci wrote that some reported vaccine effects “theoretically could be associated with miscarriage in the 1st trimester.” 

In a video posted August 10 on Fox News Digital, Johnson said these texts showed Fauci knew about miscarriage risks that health officials weren’t publicly acknowledging at the time.

Citing a 2021 study of pregnant women who received the vaccine, Johnson said the study found “an 82 percent miscarriage rate with women who got the injection in the first or second trimester.” 

But a look at the April 2021 findings, which were published in the New England Journal of Medicine, shows that Johnson misrepresented the data. His statement ignores numerous studies showing the vaccine is not associated with a heightened risk of miscarriage. 

Johnson’s spokesperson Grace Carnathan said Johnson was quoting from a 2022 open letter by Dr. James Thorp, an OBGYN who has argued that COVID-19 vaccines increase miscarriage risk. Asked for additional data, Carnathan pointed PolitiFact back to Fauci’s text messages. 

“These records show that Dr. Fauci was worried about the potential of miscarriages following COVID-19 vaccination,” Carnathan said.

The Fauci messages

Released August 10 by Johnson and Sen. Rand Paul, a Kentucky Republican, Fauci’s text message chains include a January 2021 conversation Fauci had with Drs. Vivek Murthy, then the nominee for surgeon general, and Rochelle Walensky, director of the Centers for Disease Control and Prevention. 

Shortly after mRNA COVID-19 vaccines became available for some members of the public, Fauci responded to a question from Murthy about vaccination timing during pregnancy. First, Fauci said there is no theoretical reason to favor early vaccination over late vaccination. In the next text, Fauci said certain reported side-effects “theoretically could be associated with miscarriage in the 1st trimester.”

Fauci’s message reflected early speculation before there was clear data on vaccination and pregnancy. Later studies found that the vaccine does not create a heightened risk for miscarriage. 

Johnson misrepresents 2021 vaccine study

The New England Journal of Medicine’s paper that Johnson pointed to was a preliminary report conducted by the CDC’s v-safe COVID-19 Pregnancy Registry Team.

The paper’s researchers contacted 3,958 people who had been vaccinated while pregnant or shortly before conceiving.

About three months after they had received the vaccine, 712 of those people had given birth to healthy babies, 104 experienced miscarriages and one had a stillbirth. Ten people had ectopic pregnancies or induced abortions. The remaining 3,131 participants were either still pregnant or had not yet completed follow-up.

Researchers initially found 104 miscarriages out of 827 completed pregnancies, a 12.6 percent miscarriage rate. But in a September follow-up, they acknowledged that because 700 of those 827 pregnant women received the vaccine when they were already in their third trimester, 827 was not a useful denominator. 

(For comparison, the miscarriage rate for all known pregnancies is estimated to be between 10 percent and 20 percent.)

Here’s the error that led to Johnson’s problematic 82 percent statistic:

Johnson said in the video that the 700 of those 827 pregnant women who received the vaccine when they were already in their third trimester should not be counted. So, he changed the denominator by excluding those 700 to calculate a new miscarriage rate of about 82 percent.

But that new denominator, 127, represented only early-vaccinated women whose pregnancies had already ended by the time of the study’s cutoff — not all of the 3,958 people who had been vaccinated in the first two trimesters. Most of the remaining participants who had been vaccinated early were still pregnant and not considered in the study.

Updated study finds no increased miscarriage risk 

A September 2021 follow-up examining the same registry surveyed 2,456 people who had been vaccinated shortly before conception or before 20 weeks’ gestation. The study tracked the cumulative miscarriage risk, which adjusted for the vaccines’ timing. 

The study found a cumulative miscarriage risk between 12.8 percent and 14.1 percent, depending on how it was calculated — well within the typical range.

Dr. Krutika Kuppalli, an infectious disease doctor and professor at the University of Texas Southwestern Medical Center, said in a social media post August 11 that numerous studies have shown vaccines do not increase miscarriage rates.

“Studies involving more than 1 million pregnancies worldwide have likewise found no increased risk of miscarriage, stillbirth, preterm delivery, or birth defects,” Kuppalli said, pointing to the CDC’s page on COVID-19 vaccination for pregnant women.

Some of them include:

• A 2021 study compared the pregnancies of more than 100,000 women and found that miscarriage was no more likely in women who had been vaccinated in the past 28 days, compared with those who had not. 
• A 2023 analysis of 21 different studies involving more than 123,000 pregnancies found no increased miscarriage risk after vaccination.
• A March 2026 study revisited the data from the COVID-19 Vaccine Pregnancy Registry and tracked pregnancy outcomes of 12,097 women who received the COVID-19 vaccine before 20 weeks’ gestation. The researchers found the cumulative miscarriage risk, including before six weeks, was 13.5 percent, in line with the standard estimates. 

The American College of Obstetricians and Gynecologists recommends COVID-19 vaccination for people who are pregnant and considering pregnancy and says “the science has not changed,” despite changing federal guidance. 

Our ruling 

Johnson said the COVID-19 vaccines were associated with an “82 percent miscarriage rate with women who got the injection in the first or second trimester.” 

Johnson pointed to an often-miscited study, and misrepresented what the study found. Numerous studies in the last five years have found no increased risk of miscarriage in people who received the COVID-19 vaccine. 

PolitiFact rates the statement False.