Study Finds COVID-19 Vaccination During Pregnancy Does Not Increase Risk of Preterm Birth or Stillbirth

New research indicates that COVID-19 vaccinations did not increase the risks of preterm births or gestational issues for pregnant women, despite prior conflicting evidence.

A new study published in BMJ found that getting vaccinated against COVID-19 while pregnant was not associated with a higher risk of preterm birth, small for gestational age at birth, or stillbirth.

The research contrasts existing evidence that COVID-19 vaccination during pregnancy may increase the risks of adverse maternal, fetal, and neonatal outcomes, according to the study authors.

They noted there is limited evidence about pregnancy outcomes and COVID-19 vaccinations. Studies have shown that catching COVID-19 while pregnant is associated with a greater risk of hospital admittance and death in the mother, as well as preterm birth and stillbirth. The vaccine has been found to be an effective measure against contracting the virus in both mother and newborn.

A team of Canadian scientists sought to address the lack of information in this population by assessing the risk of a pregnant women having a preterm birth, small for gestational age at birth, or stillbirth after receiving a COVID-19 vaccination.

Researchers examined more than 85,000 births from a population-based birth registry in Ontario, Canada between May 1 and December 31, 2021. They identified liveborn and stillborn infants who were either gestationally aged 20 weeks and up to or born at least 500 g.

Other accounted factors included the mother’s age at delivery, pre-pregnancy body mass index (BMI), reported smoking or substance use during pregnancy, pre-existing health conditions, number of previous live births and stillbirths, area of residence, and income. The investigators then linked this information to a database with information on COVID-19 vaccinations in Ontario.

Among patients, 43,099 had 1 or more COVID-19 vaccinations while pregnant. More than 99% received an mRNA vaccine—mainly Pfizer-BioNTech or Moderna.

The researchers found no association between vaccination and risk of premature birth. Among preterm births, 6.5% occurred in vaccinated women and 6.9% in unvaccinated women. Spontaneous preterm births averaged 3.7% and 4.4% in vaccinated and unvaccinated women, respectively, and very preterm births occurred in 0.59% and 0.89%, respectively.

Researchers did not find an increased risk for having babies who were small for their gestational age at birth due to the vaccine. Small births occurred in 9.1% of vaccinated women and even more in unvaccinated individuals at 9.2%.

Additionally, the investigators observed that the trimester in which a pregnant woman was vaccinated did not matter—the risk of preterm birth was not greater. Neither the number of doses received, nor the type of mRNA vaccine impacted these risks any more than not being vaccinated at all.

“Our findings can inform evidence-based decision making about COVID-19 vaccination during pregnancy,” the study authors said in the press release.

The study cannot establish causation because it is observational. The researchers said they were further limited to assessing mRNA vaccines, along with the inability to assess vaccination before pregnancy or at conception.

“Future studies to assess similar outcomes after immunization with non-mRNA COVID-19 vaccine types during pregnancy should be a research priority,” they added.


No link between covid-19 vaccination in pregnancy and higher risk of preterm birth or stillbirth. EurekAlert! August 17, 2022. Accessed on August 28, 2022.

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