People who are infected with the virus that causes Covid-19 while pregnant face a higher risk of having a very preterm birth, as well as any preterm birth, according to a large US study published in The Lancet Regional Health - Americas journal.
The researchers at University of California (UC) San Francisco in the US found that 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.
The risk of any preterm birth or giving birth at less than 37 weeks was 40 per cent higher in those with the SARS-CoV-2 infection, they said.
For those who also had hypertension, diabetes and/or obesity as well as Covid-19, the risk of preterm birth rose 160 per cent, according to the study.
"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 study lead and corresponding author Deborah Karasek, an assistant professor at UC San Francisco.
"Our results point to the importance of preventative measures to reduce Covid-19 infection among pregnant people to prevent preterm birth, including vaccination," she said.
Pregnant people are considered a high-risk population for Covid-19 infection, the researchers said.
The study identifies the risks of Covid-19 by specific subtype of preterm birth, as well as by race, ethnicity, and insurance status.
The researchers also found that 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 instance, 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 pre-term 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 prioritised, with supportive policies to reduce exposure and stress, and increase access to care," she said.
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, they said.
According to the study, 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 the disease.
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.
The researchers noted that 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 the disease, they said.
Researchers found that preterm birth rates did not vary by whether the births were spontaneous or medically-indicated, which may suggest multiple pathways between Covid-19 diagnosis and preterm birth.
They acknowledged some limitations of the study, which 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, Karasek added.