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A new, large study finds no link between adverse birth outcomes and COVID-19 vaccination during pregnancy. LAKRUWAN WANNIARACHCHI/AFP via Getty Images
  • COVID-19 during pregnancy has associations with an increased risk of adverse health outcomes, including maternal mortality and preterm birth.
  • Yet vaccination rates in pregnant people remain low owing to concerns about the safety of COVID-19 vaccines.
  • A large Centers for Disease Control and Prevention (CDC) study involving over 40,000 pregnant women shows that receiving a COVID-19 vaccine during pregnancy did not increase the risk of adverse birth outcomes such as preterm birth and smaller size than usual at birth.
  • This study, along with previous research, suggests that COVID-19 vaccines do not adversely impact the health of pregnant women or newborns.

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Pregnant women with COVID-19 are at a higher risk for severe illness and death than nonpregnant individuals. Yet, according to the CDC, only 41% of pregnant women have received vaccination against COVID-19.

This is despite guidance from the CDC and other medical organizations, such as the American College of Obstetricians and Gynecologists, recommending vaccination against COVID-19 for pregnant individuals.

The lower vaccination rate in pregnant women reflects their concerns about the safety of COVID-19 vaccines.

A large CDC study now adds to previous research showing that receiving a COVID-19 vaccine during pregnancy does not adversely affect the health of the newborn.

The study’s co-author, Dr. Heather Lipkind, a professor at Yale School of Medicine, said, “This CDC study of more than 40,000 pregnant women adds to the evidence supporting the safety of COVID-19 vaccination during pregnancy. This study found that COVID-19 vaccination during pregnancy was not associated with preterm birth or small-for-gestational-age (SGA) when comparing vaccinated with unvaccinated. This study adds to the evidence that COVID-19 vaccination is safe during pregnancy.”

The study appears in the CDC’s weekly journal Morbidity and Mortality Weekly Report.

The clinical trials that researchers conducted to test the safety and efficacy of COVID-19 vaccines did not involve pregnant people.

However, subsequent studies showed no obvious safety concerns associated with COVID-19 vaccines on the health of pregnant people or newborns.

Yet many of these studies have involved a small sample size or lacked a control group of unvaccinated pregnant individuals.

The present study investigated the impact of COVID-19 vaccination during pregnancy on birth outcomes while addressing these shortcomings.

To study the impact of vaccination on birth outcomes, the researchers compared the rates of preterm birth and SGA at birth for vaccinated and unvaccinated pregnant women.

Preterm birth refers to the baby being born before 37 weeks of pregnancy. In contrast, SGA at birth describes babies who are smaller or less developed than 90% of newborns of the same gestational age. Gestational age refers to the duration of pregnancy, starting from the time of the person’s last period.

The researchers examined the effects of vaccination on preterm birth and SGA due to the association of these factors with an increased risk of mortality and adverse health outcomes for the newborn.

The researchers estimated preterm birth and SGA at birth rates using birth records and electronic health data from Vaccine Safety Datalink. Vaccine Safety Datalink is a collaboration between CDC and nine health care organizations. It uses electronic health records from participating healthcare sites to assess the safety of vaccines.

The present study involved 46,079 pregnant women aged between 16 and 49 years, whose pregnancies were estimated to have started between May and October 2020.

Of the unvaccinated pregnant women, 38.4% were Hispanic, 32.2% were white, non-Hispanic, 15.7% were Asian, non-Hispanic, and 9.1% were Black, non-Hispanic. In the vaccinated pregnant women group, these percentages were: 24.5, 43, 25.6, and 2.7, respectively.

The researchers found that only around 21% of the pregnant women from the study had received at least one dose of the COVID-19 vaccine between December 2020 and July 2021.

Most of them received the Pfizer (54.4%) or Moderna (41.4%) mRNA vaccines, while only 4.2% had received the Johnson & Johnson vaccine. Over 98% of these women received the first dose of the COVID-19 vaccine in either the second or third trimester of their pregnancy.

After controlling for variables, the researchers found that the prevalence of preterm birth and SGA at birth was similar in vaccinated and unvaccinated pregnant women.

Moreover, the trimester when the participant received the first or only COVID-19 dose did not impact the risk of preterm births or SGA at birth. Similarly, the number of mRNA vaccine doses that individuals received during pregnancy did not influence the prevalence of these adverse birth outcomes.

Medical News Today spoke to Dr. Deshayne Fell, an associate professor at the University of Ottawa, Canada. Dr. Fell, who was not involved in the study, said, “From other studies of [SARS-CoV-2] infection over the past 18 months, we know that there is an increased risk of preterm birth, in particular, following [SARS-CoV-2] infection during pregnancy.”

“So, this study by Lipkind et al. provides excellent evidence that COVID-19 vaccination is not associated with preterm birth, and this information can be used to help support people’s decision-making about COVID-19 vaccination during pregnancy. It is also very reassuring for those who have already been vaccinated during pregnancy.”

“This report on a very well-done study provides strong evidence against there being any unanticipated adverse effects of COVID-19 vaccination on birth outcomes. The study is quite large, includes a broadly representative population from multiple sites, the analyses were conducted properly to account for the time at risk of receiving the vaccine, and there was a careful adjustment for potential confounding factors.”

“With respect to the most common adverse birth outcomes related to preterm birth or restricted fetal growth, the study’s results are quite convincing,” Dr. David A. Savitz said.

Dr. Savitz is a professor of epidemiology at Brown University and was not involved with the study.

The authors of the study acknowledged a few limitations of their research. Firstly, its timing meant that it only involved a few women in the first trimester of their pregnancy. As a result, further research is necessary to understand the impact of COVID-19 vaccination during the first trimester on birth outcomes.

Secondly, the researchers used the Vaccine Safety Datalink data to identify vaccinated women. And although they accumulated vaccination data using multiple data sources, the authors noted that they could have missed some data.

An underestimation of the number of vaccinated women could have biased their results.

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