NEW YORK - Last month, doctors began testing pregnant women as they arrived for labor and delivery at two Manhattan hospitals, and found a surprisingly high number of them with coronavirus.

Of 214 expectant mothers tested over a two-week period beginning March 22, 33 of the women tested positive, or about 15 percent.

And only four of them displayed symptoms at the time of admission, meaning 29 of the women, about 14 percent of the overall group had the virus but were asymptomatic or pre-symptomatic.

Doctors involved in the study cautioned it was too soon to tell whether pregnant women have a particular susceptibility to the virus, or whether the findings indicate a higher rate of infection citywide than previously thought.

"I do think it provides some interesting food for thought in terms of what may be going on in the general population," said Dr. Dena Goffman, associate professor of obstetrics & gynecology at Columbia University Irving Medical Center.

She said the findings point to the need for universal testing of those entering the health care system, regardless of coronavirus symptoms, and of pregnant women in particular.

"Pregnant women have to come to the hospital, and there are a number of things that happen during that admission — labor, delivery, potential for surgery, then you have a second patient,” she said. "So I think there are a number of reasons why paying attention in this population makes sense."

The women tested were admitted to maternity wards at New York-Presbyterian/Columbia University Irving Medical Center and New York-Presbyterian Allen Hospital, both in upper Manhattan.