Pregnant women who are sick with the H1N1 virus, also known as swine flu, are much more likely to suffer severe illness and should be immediately treated with antiviral drugs to reduce their risk of complications and death, U.S. flu experts have ruled.

A study by doctors from the U.S. Centers for Disease Control and Prevention, published online yesterday in the medical journal The Lancet, found pregnant women with the H1N1 virus were more than four times more likely to be hospitalized than others with the illness. The authors also noted a relatively large proportion of deaths among pregnant women.

Canada has also found that pregnant women are more likely to develop complications or be hospitalized if they contract swine flu, though they are no more at risk of catching it.

Forty-five of 235 women between the ages of 15 and 50 who have been hospitalized due to the H1N1 influenza virus were pregnant. “(That) is a much higher rate than the general population, but they are small numbers still,” Chief Public Health Officer Dr. David Butler-Jones said yesterday.

Dr. Kellie Murphy, a maternal-fetal medicine specialist at Toronto’s Mount Sinai Hospital, said the hospital has adopted the CDC recommendations for treating pregnant women by giving them the antiviral drug Tamiflu at the first sign of flu symptoms.