Pregnant women who get vaccinated against influenza are less likely to have low birth weight babies, according to a study conducted in Bangladesh.
In this study, 340 pregnant women were randomly assigned to get either a flu vaccination or another vaccine.
If the period after vaccination did not include the flu season, the newborn babies weighed about the same, regardless of which vaccines their mothers received.
But study author Mark Steinhoff of the Cincinnati, Ohio, Children's Hospital says that during influenza season, the women who got the flu vaccine came down with the flu less than half as often as the women who got the other vaccine, and their babies were born at a healthier weight.
"If the mother got the vaccine and was exposed to influenza, the babies weighted 200 grams more - 3.1 kilos versus 2.9 kilos. And that is a substantial increase in birth weights," says Steinhoff, noting that it is well established that lower birth weights can have a lifetime impact.
"If there is a decreased birth weight in an otherwise healthy baby, the more it is decreased, the more likely that infant, as an adult, is likely to have conditions such as obesity, diabetes, and heart disease."
Steinhoff says he and his colleagues were the first to identify this link between flu vaccination and birth weight, but four other studies have since come up with the same findings. Still, exactly why a mother sick with flu should have a smaller baby is unclear.
"But in general terms, if the pregnant woman is sick with flu - that's an illness of a week, maybe eight days, 10 days - the baby doesn't grow as well during that time and may end up being born slightly less well-nourished."
Steinhoff stresses that the influenza vaccine is safe for mother and baby, and is one of the few vaccines that a pregnant woman can take that will protect both her and her baby.