(CNN) Pregnant women infected with the coronavirus are more likely to become severely ill and die from Covid-19, and they're at increased risk for premature delivery, according to a pair of reports released Monday by the US Centers for Disease Control and Prevention.
Although the overall risk of severe illness or death remains low, CDC researchers found that pregnant women with coronavirus are more likely to need intensive care, ventilation and heart and lung support than non-pregnant women with the virus.
A separate report found that the rate of preterm birth, when a baby is born before 37 weeks of pregnancy, is 12.9% among women with coronavirus, compared to 10.2% among the general population.
The new research adds to a growing body of evidence that pregnant women are at increased risk when it comes to coronavirus, said Dr. Denise Jamieson, chair of the gynecology and obstetrics department at Emory University School of Medicine.
"It also demonstrates that their infants are at risk, even if their infants are not infected, they may be affected," Jamieson noted on a call with reporters Monday.
For one of the reports, researchers reviewed data on 461,825 women between the ages of 15 and 44 who tested positive for Covid-19 between January 22 and October 3. They focused only on those who experienced coronavirus symptoms.
The team adjusted for outside factors and found that pregnant women were more likely to need intensive care, with 10.5 per 1,000 pregnant women admitted to the ICU, compared to 3.9 per 1,000 women who aren't pregnant.
Pregnant women were 3 times more likely to need help breathing with invasive ventilation than women who aren't pregnant. Similarly, they were at greater risk of requiring lung and heart support with oxygenation.
They were also more likely to die, with 1.5 deaths per 1,000 pregnant women, compared to 1.2 per 1,000 women who aren't pregnant.
In keeping with trends seen across the general population, researchers found some racial and ethnic minorities had an even greater potential for infection or severe disease. Among pregnant women, Hispanic women were 2.4 times more likely to die and Asian and Native Hawaiian/ Pacific Islander women had a more pronounced risk for ICU admission, they found.
The team noted that regardless of whether they were pregnant, women over 35 were more likely to experience severe illness.
The researchers said that the greater probability for severe illness among pregnant women might be due to physiological changes in pregnancy, including increased heart rate and decreased lung capacity.
"To reduce the risk for severe illness and death from COVID-19, pregnant women should be counseled about the importance of seeking prompt medical care if they have symptoms and measures to prevent SARS-CoV-2 infection should be strongly emphasized for pregnant women and their families during all medical encounters, including prenatal care visits," the team wrote.
Pregnant women with coronavirus infection were also more likely to deliver babies early, CDC researchers found.
A team studied pregnancy and infant outcomes for 4,442 women diagnosed with Covid-19 between March 29 and October 14. Among 3,912 live births, they found 12.9% were preterm. In comparison, preterm births accounted for 10.2% of live births among the general population in 2019.
The CDC says that babies who are born too early are at increased risk of death and disability, including breathing, vision and hearing problems.
Among infants tested for Covid-19, the team found 2.6% were positive. Coronavirus infection was most common in infants whose mother tested positive for the coronavirus within one week of delivery.
About 60.6% of the women experienced symptoms, though researchers say that symptom status of mothers did not impact the frequency of preterm birth among infants.
At least one underlying medical condition was reported in 45% of women, the most common being obesity.
Because 84.4% of the women studied experienced Covid-19 in their third trimester, more research is needed to understand the impact of infection in early pregnancy and the long-term effects on infants.
While severe Covid-19 does occur in newborns, the majority of those born at term with Covid-19 have asymptomatic or mild disease, the researchers noted.
Though the risk to pregnant women remains low, they should take precautions, especially as the United States enters the winter months amid rising coronavirus cases.
"Less than 1% of pregnant women with Covid are admitted to an intensive care unit," Jamieson said. "However, they are at increased risk when you compare them to their non-pregnant counterparts."
Jamieson recommends pregnant women avoid gatherings, wear masks and social distance -- even in their own households, when necessary.
"We're learning more about how people are infected, and there is some new information that household contacts -- so, people who are in your house -- may be a source of infection," she said.
"It's not unreasonable, if a person has a lot of exposure at work, for instance, for that person to stay separated from the rest of their family or to protect the rest of their family by wearing a mask or even separating physically in the house," she added.
Jamieson stressed that this year's flu vaccine will be more important than ever, especially for pregnant women. She added that once a coronavirus vaccine comes into play, it's important that pregnant women are considered in the development and distribution.
"Pregnant women need to be included in the different phases of vaccine trials, so that when a vaccine is available we understand the safety and efficacy of vaccines in pregnancy," she said.
"It's really important that when there's a vaccine available that pregnant women are not denied the opportunity to be vaccinated," Jamieson added.