Still, many pregnant patients who are reluctant to introduce foreign substances into their bodies want more long-term data and scientific evidence that the vaccines have no effect on the development of the fetus, said Dr. Adam Urato, a Framingham, Massachusetts maternal-fetal medical specialist providing advice to patients about the vaccine.

“The only question my patients ask me all the time is, ‘Are we absolutely sure that these vaccines won’t harm my baby?'” He said.

Tista Banerjee, 32, who gave birth to twins in late June, said she chose not to get vaccinated until after she was pregnant.

“During pregnancy, they say that if you don’t need to take external medication, then you shouldn’t and that you should be extra careful with what you put into your body,” said Ms. Banerjee. The vaccine was still fairly new in April when she was considering vaccinating, she said, and she was lucky enough to be able to work remotely and avoid unnecessary exposure to the virus.

She was fully vaccinated in July, shortly after giving birth, she said.

Pregnant women, who were often excluded from medical trials, were not included in the clinical trials of the Covid vaccines, and the World Health Organization was ambiguous in its guidelines on vaccines, both for breastfeeding women for whom safety data are not available, and for and for pregnant women.

In interim recommendations issued in June, the global health organization said it recommends vaccination “when the benefits of vaccination to the pregnant woman outweigh the potential risks.” Examples were women who are at high risk of exposure to Covid and those with chronic health conditions such as obesity or diabetes who are at higher risk for serious illness.

Sabrina Imbler contributed the reporting.