About 30 percent of pregnant women in the United States remain unvaccinated, according to estimates from the C.D.C.

“We know pregnant individuals are at an increased risk when it comes to Covid-19, but they absolutely should not and do not have to die from it,” said Dr. Christopher Zahn, chief of clinical practice and health equity and quality at the American College of Obstetricians and Gynecologists.

Kaiser researchers found that among women who were pregnant or planning to become pregnant: 60 percent believed that pregnant women should not get the vaccine, or were unsure if this was true; and about the same number believed, or were unsure, whether the vaccines had been shown to cause infertility. While only 16 percent said they believed the false infertility claim outright, another 44 percent said they were unsure if it were true.

Torrents of misinformation during the pandemic have repeatedly disrupted public health campaigns. Previous spikes in falsehoods spread doubts about vaccines, masks and the severity of the virus, and undermined best practices for controlling the spread of the coronavirus, health experts said, noting that misinformation was a key factor in vaccine hesitancy. Dr. Vivek Murthy, the U.S. surgeon general, has demanded information from tech companies about the major sources of Covid-19 misinformation.

One reason misinformation about the vaccines and pregnancy may have gained so much traction, experts say, is that the earliest clinical trials of the coronavirus vaccines excluded pregnant women. The lack of trial data led the C.D.C. and World Health Organization to initially give different recommendations to pregnant women, though neither explicitly forbade, nor encouraged, immunizing pregnant women. Other health organizations chose to wait for more safety data from later trials before making an official recommendation for pregnant women to get vaccinated.

“Unfortunately, in the interim, the information gap was filled with a lot of misinformation, particularly on social media, and that has been an uphill battle to combat,” Dr. Zahn said. “While we have made a lot of progress with uptake among pregnant individuals in the last year, there was also a lot of time lost.”

Researchers have pointed for years to the proliferation of anti-vaccine misinformation on social networks as a factor in vaccine hesitancy and in the lower rates of Covid-19 vaccine adoption in more conservative states.

“At the root of this problem is trust, or really, it’s a lack of trust,” Dr. Sell said. “Trusted doctors need to help support women in understanding the importance of vaccination against Covid as well as its safety. But when people don’t have trust in authorities, no provider to go to, or generally don’t feel like they have a place to get good information, this misinformation can fill that void.”