MARIA CHENG,AP Medical Writer

LONDON (AP) ó Pregnant women who get swine flu are at least four times as likely to be hospitalized as other people with the virus, a new study says.

While experts don’t know if pregnant women are more susceptible to swine flu, they say once pregnant women are infected, they have a higher risk of complications.

Researchers at the U.S. Centers for Disease Control and Prevention analyzed the first 34 U.S. cases, including 6 deaths, of swine flu in pregnant women from April to mid-June.

They concluded that pregnant women suspected of having swine flu should be given Tamiflu as soon as possible, even before tests confirm the diagnosis. The experts also recommended that pregnant women be among the first in line when a vaccine is expected to be ready in the fall.

The study was published online Wednesday in the medical journal, the Lancet.

Like the general population, most pregnant women who get swine flu only have mild symptoms like fever and a cough, according to the World Health Organization. Denise Jamieson of the U.S. CDC, the study’s lead researcher, said the agency doesn’t recommend any special precautions for pregnant women to avoid catching the virus.

But if pregnant women do get swine flu, Jamieson said doctors need to act fast, preferably within 48 hours of developing symptoms.

“The message is don’t delay appropriate treatment because she’s pregnant,” she said.

Health officials at WHO have previously reported that some doctors were reluctant to give the antiviral drug Tamiflu to pregnant women. While safety data on Tamiflu use in pregnant women is limited, Jamieson said it appears relatively safe.

Of the six fatal cases in the Lancet study, Jamieson said nearly all had viral pneumonia before experiencing acute respiratory problems, and were put on ventilators before they died. Aside from one woman who had asthma and another who was obese, Jamieson said the women were essentially healthy.

U.S. guidelines list pregnant women as a high-priority group for pandemic vaccines, although that is for vaccines without adjuvants, ingredients used to stretch a vaccine’s active ingredient.

In the U.S., flu vaccines don’t have adjuvants, but in Europe, many do. There is little data on how safe vaccines with adjuvants are in pregnant women.

Cecilia Nwobi, a London-based lawyer pregnant with her third child, said she hasn’t yet decided if she will get a swine flu shot.

“People don’t want to be guinea pigs for something that hasn’t been tested in pregnant women,” she said. “But if I’m faced with a more serious situation later, I might feel differently.”

Advice from European authorities has varied widely ó some British and Swiss officials even initially advised that women consider delaying having children until the pandemic ends ó even though that might be more than a year away.

Britain’s department of health quickly backed away from that stance, although it still says pregnant women may want to avoid crowded places.

“The most important measures are for pregnant women to observe good hand and respiratory hygiene,” said Dr. Boon Lim, a spokesman for Britain’s Royal College of Obstetricians and Gynaecologists. “But if the situation worsens, further advice may be necessary.”