Study Finds COVID-19 Vaccination in Pregnancy Lowers Risk of Preterm Births

Yet another reason to make sure you get vaccinated against COVID-19, especially if you are pregnant.

Fact checked by Sarah Scott

While the pandemic may be behind us, we may not want to hear it, but COVID-19 is still hanging around. The risks are very real for pregnant people. But there's new research that shows promise for those pregnant people who get the COVID vaccine.

As researchers who study factors that shape health at birth, Florencia Torche, PhD, Dunlevie Family Professor of Sociology at Stanford University, and Jenna Nobles, PhD, Professor of Sociology at the University of Wisconsin-Madison, soon realized after the onset of the pandemic that one of the most enduring legacies of COVID may be its effect on infant health.

Pregnant people are considered a vulnerable population which means COVID can have serious effects on them and their fetuses. Pregnant people are more at risk for preeclampsia, ICU hospitalization, and death, Torche says, and babies are more likely to be born before 37 weeks and need intensive care.

“COVID-19 affects multiple biological systems and there are likely several processes in play,” Torche says. “We know that infections trigger immune and inflammation responses, and we have evidence now that COVID-19 can cause disintegration of the placenta. These, among other processes, can lead to preterm birth."

When the COVID vaccine became available, it was a significant moment for vulnerable populations, pregnant people included.

"So we set out to understand how the availability of vaccines and the decision to use them may have reduced a serious health burden for the next generation of U.S. children,” Nobles says.

The Risk of Preterm Birth

Preterm birth is defined as a birth that occurs before 37 weeks gestation and is one of the leading causes of infant mortality in the United States. Not having enough time in the womb can also lead to more costly medical procedures and attention once born.

“Preterm birth is associated with immediate health risks for newborns; conditions like respiratory problems, infection, and neurological issues in the first days, weeks, and months of life,” says Kimberly B. Glazer, PhD, MPH, the Director of OBGYN Resident and Fellow Research at the Blavatnik Family Women’s Health Research Institute. “Critically, racial disparities in preterm birth drive persistent and alarming infant health inequities in the U.S., with the highest rates of preterm birth among Black and Indigenous infants.”

Rates of preterm birth increased by 4% from 2020 to 2021, the height of the pandemic. In general, Black women were more likely than white or Hispanic women to experience a preterm birth, and the presence of COVID only exacerbated that disparity.

The Effect of the COVID-19 Vaccine on Pregnant People

The rate of preterm births may have increased significantly in 2021 as COVID continued to wreak havoc on the world. But by 2022, as the COVID vaccine became widely available, Torche and Nobles noticed that those numbers were dropping again. So they set out to study if and how the vaccine had anything to do with the decrease.

The researchers chose to use birth records data based on birth certificates in California. That's because the state provides information on all births that occur so they did not have to worry about selectivity of small samples skewing their findings. The duo compared birth record data with vaccination rate data across the state to see if preterm birth rates were lower in communities with higher vaccination rates.

“Our analysis compared the probability of preterm birth between siblings,” says Torche. “That is, it compared newborns whose mothers had a COVID-19 infection during pregnancy with their siblings who did not experience a maternal COVID infection. Because this method compares births to the same mother, it 'controls for' any differences between women that could otherwise account for differences in preterm births.”

Their findings show the risk for pregnant people in California of having preterm birth was as high as 12.3% between July and November 2020, compared to a 6.9% risk among older siblings born to the same mother pre-pandemic. By January 2022, the impact of COVID on preterm birth significantly decreased, but people who lived in areas with high vaccination rates saw those effects a year earlier compared with zipcodes with lower vaccination rates.

"Our findings suggest what will actually be harmful to newborns is [pregnant people] not receiving a vaccine."

Jenna Nobles, PhD

What This Means for Pregnant People

The main takeaway for pregnant people is to get the COVID vaccine and updated boosters, when available. But despite the availability of vaccines to prevent serious complications from the infection, there are barriers some pregnant people face with receiving the shots.

Dr. Glazer says that includes "misinformation and misperceptions" about the safety of the vaccine, despite the support from major professional obstetric and pediatric organizations.

“It is really important to remember that vaccination rates are lowest among minoritized and marginalized communities, who face maternal and infant health crises in the United States," says Dr. Glazer. "Vaccine uptake overall, and specifically for the most recent boosters, is much lower among Black and Hispanic pregnant people compared to white individuals. Entrenched racism and bias in the health care system have contributed to distrust of and lower engagement in medical care among these communities. Issues of access are also critical—such as having time off work or transportation to health centers. We can do more to address these barriers to improve equity in vaccine coverage.”

Barriers aside, many pregnant people express worries about the safety of the vaccine itself. As Dr. Glazer explains, pregnant people are already being told so much about what they should or shouldn’t do, and sorting through misinformation about the vaccine can be overwhelming.

“Pair this with the fact that pregnant individuals were not included in initial COVID-19 vaccine trials, and the considerable mixed messaging about safety for pregnancy and reproductive health in the earlier stages of vaccine rollout, and the hesitancy is understandable,” Dr. Glazer says. “However, substantial evidence supports the safety of vaccination in reproductive age and pregnant populations.

Nobles also points out that another reason for pregnant people’s hesitancy with receiving the vaccine is its safety for the unborn baby.

“Our findings suggest what will actually be harmful to newborns is not receiving a vaccine,” Nobles says. “This is useful information that could be shared by healthcare providers with pregnant patients and people intending pregnancy.”

While more research needs to be done on COVID’s impact on birthing people overall, but also on how preterm labor can continue to be prevented, Torche, Nobles and Dr. Glazer all agree that the COVID vaccine is a safe and effective option for pregnant people.

“Beyond safety, COVID-19 vaccines offer effective protection against major risks to both mom and baby,” Dr. Glazer explains. “Getting vaccinated is something everyone can do to increase their chances of a healthy pregnancy and birth.”

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