Pregnant women are four times more likely to be hospitalised with swine flu than the general population, America's public health agency has warned.
In the first two months of the pandemic from mid-April to mid-June there were six deaths from swine flu among pregnant women reported to the Centers for Disease Control and Prevention in Atlanta, all of whom were "relatively healthy", the agency said.
There were 34 cases of swine flu among pregnant women within the first month, of whom a third (11) were admitted to hospital.
Writing in The Lancet, Denise Jamieson and colleagues from CDC say the the four-fold higher admission rate is in line with previous evidence suggesting pregnant women are at higher risk of complications.
Pregancy reduces immunity in women, to avoid rejection of the developing foetus, and in the later stages the growing foetus can press on the diaphragm reducing lung capacity and increasing the risk of pneumonia.
None of the women who died were treated with anti-viral drugs and many of those who contracted swine flu were also untreated. This may have been because health workers were reluctant to give the drugs to pregnant women for fear of harming the baby, or that the women themselves were reluctant to take them.
This is a mistake, the authors say. They admit information about the safety of anti-viral drugs in pregancy is limited but, given the known threat from swine flu, "the benefits of treatment with these drugs are likely to outweigh potential risks to the fetus."
In the UK, the Government recommends pregnant women take Relenza, which is inhaled direct to the lungs where it's needed, so a smaller dose is required. Tamiflu, which is taken orally as a pill, is absorbed throughout the body, requiring a larger dose for the same effect on the lungs.
Antiviral drugs reduce complications of flu as well as marginally shortening the illness, and should be given within 48 hours of the onset of symptoms to have maximum benefit.
The authors say: "Although the decision to admit a pregnant woman is complex and might include considerations beyond simply the severity of disease, that a high proportion of influenza-related deaths in the USA have been in pregnant women is concerning."
The greater vulnerablity of women to flu during pregnancy means they should be treated with antiviral drugs as soon as possible after developing symptoms, and they should be among the first to be offered a vaccine when one becomes available.
Antiviral drugs reduce complications of flu as well as marginally shortening the illness, and should be given within 48 hours of the onset of symptoms to have maximum benefit.Reuse content