Pregnant women who had Covid-19 when they delivered their babies were almost twice as likely to have a stillbirth as healthy women who did not have Covid, according to a Centers for Disease Control study released on Friday that examined more than 1.2 million deliveries in the United States from March 2020 to September 2021.
While stillbirths were rare overall, representing less than 1 percent of all births, 1.26 percent of the 21,653 women with Covid experienced a stillbirth, compared with 0.64 percent of women without Covid. Even after adjustments were made to control for differences between the groups, women with Covid were 1.9 times as likely as healthy women to have a stillbirth.
The risk of stillbirth has been even higher for women with Covid since the Delta variant has been dominant: While the risk of stillbirth for women with Covid was 1.5 times as high as that of healthy women before July, when Delta became dominant, it was four times as high from July to September. As many as 2.7 percent of deliveries to women with Covid were stillbirths during the period studied while Delta was dominant.
“There had been reports suggesting an increased risk, but stillbirths are hard to study, because luckily they are uncommon,” said Dr. Denise Jamieson, the chief of gynecology and obstetrics at Emory Healthcare. “This is some of the strongest evidence of the increased risk, and probably the strongest data pointing to the risks specifically tied to Delta.”
The C.D.C. strongly encourages pregnant and breastfeeding women and women planning or trying to become pregnant to be vaccinated against Covid, but resistance has been strong, even though pregnancy is on the C.D.C.’s list of health conditions that increase the risk of severe disease.
Studies have shown that pregnant patients who are symptomatic are more than twice as likely as other symptomatic patients to require admission to intensive care or interventions like mechanical ventilation, and they may be more likely to die. They are also more likely to experience a preterm birth.
Another C.D.C. study issued on Wednesday described the cases of 15 pregnant women in Mississippi who died of Covid during their pregnancy or shortly afterward, including six who died before the Delta variant became dominant and nine who died from July to October, while Delta was dominant.
Of the women who died, nine were Black, three were white and three were Hispanic. The median age was 30. Fourteen of the women had underlying medical conditions, and none were vaccinated. Five of the deaths occurred before vaccinations were available.