(AP) -- Swine flu is not only dangerous to pregnant women, but it's a threat to new mothers too, the first study to document this risk shows. An analysis of pregnant women and new mothers who were hospitalized with swine flu in California found that those who had a baby in the previous two weeks were at higher risk of severe flu complications.
The swine flu threat to pregnant women has been well-documented, and public health officials urged them to get vaccinated. Previous research showed expectant mothers infected with the virus are more likely to be hospitalized and face a greater risk of death than the general population.
The new report, released Wednesday by the New England Journal of Medicine, is the first to look at the risk to women who recently gave birth and highlights "the continued high risk immediately after pregnancy," the researchers wrote.
As a result of the research, the Centers for Disease Control and Prevention recently revised its guidelines, recommending that flu drugs be given to women who show signs of the flu soon after they give birth.
The study was done by the California Department of Public Health and the CDC. California, the nation's most populous state, has stepped up surveillance of the disease since the 2009 H1N1 strain was discovered in April in two California children.
The study involved 94 pregnant women and eight new mothers who were hospitalized during the first four months of the pandemic before a vaccine became available, in October.
Most of those pregnant women were in their second or third trimesters, when the risk of flu complications is believed to be highest. Many were otherwise healthy and went to the hospital with mild symptoms like fever or cough, but their health rapidly declined.
A total of 22 women - 18 pregnant and four who had delivered - needed intensive care. Eight died including two new mothers. The study found all eight women who died did not receive prompt treatment with flu drugs.
Researchers estimated that swine flu killed more than four pregnant women per 100,000 live births in California. The pandemic has proven so deadly to pregnant women that researchers say it may increase the nation's overall maternal mortality for 2009. The rate was 13.3 deaths per 100,000 live births in 2006, the latest year for which data was available.
Death from childbirth remains fairly rare in the United States. One of the most common causes is excessively bleeding.
"This is unusual in that an infectious disease may increase the overall mortality rate," said Dr. Denise Jamieson of the CDC, who was part of the study.
In a separate study also appearing in the journal, doctors in Argentina determined the death rate from swine flu in children was 10 times higher than in a normal flu season. More than two-thirds of children who died had chronic health problems.
Explore further: Flu drug advised for pregnant women with swine flu
New England Journal: http://www.nejm.org
CDC advice: http://www.cdc.gov/h1n1flu/pdf/tip-sheet-pregnant.pdf