Pregnant women infected with the new H1N1 swine flu have a much higher risk of severe illness and death, U.S. government researchers said on Wednesday, confirming a trend that has worried global health experts.

While pregnant woman have always had a higher risk of severe disease from influenza in general, the new H1N1 virus is taking an exceptionally heavy toll, the researchers said.

"We do see a fourfold increase in hospitalization rates among ill pregnant women compared to the general population," Dr. Denise Jamieson of the U.S. Centers for Disease Control and Prevention said in a telephone interview.

"We're also seeing a relatively large proportion of deaths among pregnant women. We report 13 percent in the paper, but that is a very unstable number based on a small number of deaths reported," said Jamieson, whose study appears in the journal Lancet.

The study was based on the deaths of six pregnant women out of 45 deaths related to H1N1 reported to the CDC between April 15 and June 16.

All of the women were healthy prior to infection, and all developed pneumonia and needed to be put on a ventilator.

Jamieson said 302 deaths have been officially reported to the CDC from the new H1N1 virus.

"Among those, we have relatively complete information on 266 deaths. And of those, 15 have been among pregnant women, which is about 6 percent," Jamieson said.

Given that at any point, about 1 percent of the U.S. population is pregnant, she said, pregnant women "are definitely over-represented in terms of the proportion of deaths."

She said pregnant women do not need to change the way they live because of the new H1N1 flu.

"There is no reason to delay pregnancy or to be overly concerned. We do not have evidence that pregnant women have increased susceptibility or are more likely to acquire influenza," Jamieson said.

"It's just that when they have influenza they are at increased risk of having severe disease," she said.

Jamieson said pregnant women who suspect they have influenza should call their doctors promptly.

And she said doctors need to provide a separate waiting area for pregnant women who suspect they are ill, to protect healthy pregnant women from infection.

Jamieson said pregnant women with influenza should be given antiviral drugs as soon as possible, within the first 48 hours to be most effective.

Despite recommendations from the Advisory Committee on Immunization Practices and the American College of Obstetricians and Gynecologists that all pregnant women get a seasonal flu shot, less than 14 percent do, according to the CDC.

The ACIP, which advises the CDC, is meeting later on Wednesday to decide who should be first to get the new H1N1 vaccine.

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