The report found that older women and teenagers were most likely to have a low birth weight baby.

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Women with both disease also had a higher risk of developing anaemia, miscarrying, having a low birth weight baby and delivering prematurely.

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Experts hope to reduce this figure to 15% by 2010 as women who smoke while pregnant are three times more likely to have a low birth weight baby.

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Alternatively, a depressed mother may be more likely to produce a child who is prone to depression - and to have a low birth weight baby because they may be more likely to smoke and drink during pregnancy.

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Dr Wang is seeking to identify specific genetic traits that make women more likely to give birth to a low birth weight or premature baby.

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