Federal health officials on Wednesday bolstered their recommendation that pregnant people be vaccinated against Covid-19, pointing to new safety data that found no increased risk of miscarriage among those who were immunized during the first 20 weeks of gestation.
Earlier research found similarly reassuring data for those vaccinated later in pregnancy.
Until now, the Centers for Disease Control and Prevention has said the vaccine could be offered during pregnancy; the recent update in guidance strengthens the official advice, urging pregnant people to be immunized.
The new guidance brings the C.D.C. in line with recommendations made by the American College of Obstetricians and Gynecologists and other medical specialty groups, which strongly recommend vaccination.
“At this time, the benefits of vaccination, and the known risks of Covid during pregnancy and the high rates of transmission right now, outweigh any theoretical risks of the vaccine,” Sascha R. Ellington, an epidemiologist who leads the emergency preparedness response team in the division of reproductive health at the C.D.C.
The risks of having Covid-19 during a pregnancy are well-established, she said, and include severe illness, admission to intensive care, needing mechanical ventilation, having a preterm birth and death.
So far, there is limited data on birth outcomes, she added, since the vaccine has only been available since December. But the small number of pregnancies followed to term have not identified any safety signals.
Pregnant women were not included in the clinical trials of the vaccines, and uptake of the shots has been low among pregnant women. The majority of pregnant women seem reluctant to be inoculated: Only 23 percent of pregnant women had received one or more doses of vaccine as of May, a recent study found.
Dr. Adam Urato, a maternal-fetal medicine specialist in Framingham, Mass., who counsels patients about the vaccine almost daily, said pregnant women are very wary of exposure to synthetic chemicals and want more solid scientific evidence that the vaccines are safe.
“The one question my patients ask me all the time is, are we absolutely sure that these vaccines won’t affect my baby?” he said.