One of the largest studies of its kind suggests that most pregnant women who become infected with the coronavirus will have mild cases but suffer prolonged symptoms that may linger for two months or longer in some cases.

The study, published in the journal Obstetrics and Gynecology, found that most women who participated had mild cases of covid-19 — a finding consistent with previous studies. Among the nearly 600 women followed, only 5 percent were hospitalized and 2 percent were admitted to intensive care units.

Despite the mildness of their cases, 25 percent of the participants continued to experience symptoms eight weeks after becoming sick. The median length of symptoms was 37 days. Although pregnancy is known to cause major changes to the immune system, the length of time for continuing symptoms was surprising, said co-principal investigator Vanessa Jacoby, vice chair of research in the obstetrics, gynecology and reproductive sciences department at the University of California at San Francisco.

“We know in most studies in the general population that if you have mild covid-19, usually your symptoms go away within the first one to two weeks,” she said. “But that is not what we found if you are pregnant.”

Months into the coronavirus pandemic, many questions remain unanswered about how the virus impacts pregnant women and their babies, including its long-term effects, said David Jaspan, chair of the obstetrics and gynecology department at the Einstein Healthcare Network in Philadelphia, who was not involved in the study.

One complication is that symptoms of the virus may overlap with symptoms of a normal pregnancy. Another, Jaspan said, is that fear of being in a waiting room and being exposed to the virus has meant fewer patients are showing up for postpartum visits.

“I think there’s a lot of unknowns,” Jaspan said.

The new research, which will follow participants for a year after their deliveries, aims to fill that gap. Launched in March, it includes 594 women who tested positive for the coronavirus between March and July.

The cohort is diverse, with participants who are 60 percent White, 31 percent Latina, and 9 percent Black. Their mean age is 31 and they live across the country, with 34 percent in the Northeast, 25 percent in the West, 21 percent in the South and 18 percent in the Midwest. Thirty-one percent work in health care.

The most common initial symptom was a cough, followed by a sore throat and body aches.

In one of the study’s main findings, just 12 percent reported fevers as among their first symptoms. That’s a significant difference from the general population infected by the virus, for whom fever is a prevalent initial symptom. It also runs counter to a common belief that testing is not necessary until fever appears.

“One of the big take-home messages we want to share with people who are pregnant is, don’t wait until you have a fever to seek evaluation for covid-19 if you have these other symptoms such as sore throat or cough,” Jacoby said. “We want to also emphasize that to health-care providers, that fever was not a common symptom at all as the first symptom.”

Other, less common initial symptoms included the loss of taste or smell, shortness of breath, a runny nose, sneezing, nausea, a sore throat, vomiting, diarrhea and dizziness.

The researchers found that three weeks after becoming sick, 52 percent of the study’s participants no longer had symptoms. By the fourth week, that number had increased to 60 percent. By the eighth week, 75 percent of participants were asymptomatic.

Jacoby said the study provides an indication of what the coronavirus may look like for pregnant women who do not require hospitalization — “the overwhelming majority of people who are pregnant.”

Read more: