According to a large study led by researchers at UC San Francisco, pregnant individuals who contract COVID-19 face a higher risk of having a very preterm birth, as well as any preterm birth.
The findings of the study were published in the journal 'The Lancet Regional Health - Americas'.
The risk of very preterm birth, which occurs at less than 32 weeks of gestation, was 60 per cent higher for people infected with COVID-19 at some point in their pregnancy, while the risk of giving birth at less than 37 weeks (all preterm births) was 40 per cent higher in those with infection.
For those who also had hypertension, diabetes and/or obesity as well as COVID-19, the risk of preterm birth rose 160 per cent.
"Preterm birth is associated with many challenging outcomes for pregnant people and babies, and very preterm births carry the highest risk of infant complications," said lead and corresponding author Deborah Karasek, PhD, assistant professor in the Department of Obstetrics, Gynecology and Reproductive Sciences, and researcher with the California Preterm Birth Initiative at UCSF.
"Our results point to the importance of preventative measures to reduce COVID-19 infection among pregnant people to prevent preterm birth, including vaccination," said Karasek.
"Pregnant people may have concerns about vaccines and the health of their baby, so being able to have an open dialogue that values those concerns, describes evidence about safety, and conveys the risks posed by COVID-19 infection during pregnancy is critically important," explained Karasek.
On July 30, the American College of Obstetricians and Gynecologists (ACOG) issued updated guidance strongly recommending that all pregnant individuals get vaccinated against COVID-19.
Pregnant people are considered a high-risk population for COVID-19 infection, yet less than a quarter have received at least one dose of vaccine, according to the US Centers for Disease Control and Prevention (CDC).
The UCSF study was the first of its kind large enough to identify the risks of COVID-19 by specific subtype of preterm birth, as well as by race, ethnicity, and insurance status.
The study data reflected both existing disparities in preterm birth rates for Black, Indigenous and other people of colour (BIPOC) compared to whites, and the known outsized burden of the pandemic on communities of colour.
Latinx, American Indian/Alaska Native, Native Hawaiian/Pacific Islander people, as well as people with public insurance, had disproportionately higher COVID-19 rates during pregnancy.
For example, while 47 per cent of pregnant people in the study overall were Latinx, they represented 72 per cent of the people with COVID-19 diagnoses.
"Given that the burden of COVID-19 is greater in these populations, as is the burden of preterm birth, it really points to the need for an equity approach," said Karasek.
"With the surge in infections and increase in the Delta variant, we must think about pregnant people, especially Black and Brown populations, as the groups that need to be prioritized, with supportive policies to reduce exposure and stress, and increase access to care," added Karasek.
The researchers analysed all live births between July 2020 and January 2021 documented by California Vital Statistics birth certificates.
Of the 240,157 recorded births, nearly 9,000, or 3.7 per cent, indicated a COVID-19 diagnosis in pregnancy. The preterm birth rate among birthing people with a COVID-19 diagnosis was 11.8 per cent compared with 8.7 per cent among those without COVID-19.
The overall sample included 47.2 per cent Latinx, 26.8 per cent white, 4.9 per cent Black, 13.2 per cent Asian, 0.03 per cent American Indian/Alaskan Native, 0.4 per cent Hawaiian/Pacific Islander and 7.3 per cent identified as other, unknown, or two or more races.
Forty per cent of people in the study had public insurance at the time they gave birth, and 15.9 per cent had hypertension, diabetes, obesity, or a combination of these.
Having comorbidities along with COVID-19 infection increased the risk of preterm birth. Individuals with hypertension, diabetes and/or obesity as well as a COVID-19 diagnosis had a 160 per cent higher risk of very preterm birth and a 100 per cent higher risk of preterm birth compared to those without comorbidities or COVID-19.
"Researchers found that preterm birth rates didn't vary by whether the births were spontaneous or medically indicated, which may indicate multiple pathways between COVID-19 diagnosis and preterm birth," concluded Karasek.
Limitations of the study included that it couldn't determine when during pregnancy the individuals contracted COVID-19, or how serious the infections were.
These are important details for understanding the mechanisms by which COVID-19 affects preterm birth risk and Karasek said they are currently being studied at UCSF and elsewhere.