The children of women who gain too much weight during pregnancy are more likely to be overweight or obese by the age of eight years, a new study has found.

This risk is also higher if the mother smokes or does not exercise during pregnancy.

According to US and Greek researchers, the number of overweight children worldwide is expected to increase by 1.3 million each year, with around 300,000 children per year becoming obese.

They decided to see if there was any link between childhood obesity and the weight a mother gains during pregnancy. They looked at 5,125 children in Greece, along with their mothers. Information on the women's pregnancies was gathered, along with the body mass index of the children when they were eight years old.

The study found that the amount of weight women gained during pregnancy was strongly associated with the risk of obesity in their children. Those who gained more than the recommended amount were much more likely to have children who were overweight or obese by the age of eight.

Physical activity levels and smoking status were also strongly linked.

However, moderate exercise undertaken by women during pregnancy was found to lower the risk of children becoming obese later.

The researchers pointed out that pregnancy ‘is a phase in a woman's life in which she develops a greater awareness about her health and has an important opportunity to amend some unhealthy habits, like smoking and alcohol consumption, to adopt a more active lifestyle, and to participate in physical activities'.

"Healthcare professionals should advise expecting mothers to limit their pregnancy weight gain to the recommended range, not to smoke and consume alcohol, and to engage in moderate exercise during pregnancy," they added.

Details of these findings are published in the journal, BMC Pregnancy and Childbirth.

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