Pregnant women are four times more likely than the general population to need hospital treatment for H1N1 swine flu, data from the US suggests.
The findings suggest pregnancy does increase the risk of complications without speedy anti-viral treatment.
It also underlines the need to ensure pregnant women are made a top priority when a vaccine becomes available.
The study, by the US Centers for Disease Control and Prevention, appears in The Lancet medical journal.
Scientists studied 34 confirmed or probable cases of swine flu infection among pregnant women.
We must remember that most pregnant women who catch the disease are likely to make an uncomplicated recovery
Department of Health