Weight gain in pregnancy 'increases child obesity risk'

Women who pile on the pounds when pregnant may be creating conditions in their womb that programme their future child for a lifetime's struggle with weight, scientists believe.

And they will not be able to blame their genes, according to the research reported online in The Lancet medical journal. Weight gain during pregnancy appears on its own to be responsible for high birthweight, the findings show.

Heavy infants are known to be predisposed to obesity in later life. They may also have an increased risk of asthma and cancer.

Previous studies have demonstrated that mothers-to-be who gain a lot of weight during pregnancy are more likely to give birth to an overweight baby. But it was not known to what extent this association could be explained by genetics and other factors besides weight gain itself.

The new research suggests that simply eating too much when pregnant, and gaining weight as a result, may be enough to put your baby at risk.

"These findings have important implications to general public health," said Dr David Ludwig, one of the US authors.

"It's appropriate for a baby to be born with some fat, but a baby born too fat indicates that the foetus developed in an abnormal environment during the most critical nine months of life."

The scientists scoured US birth records to identify mothers in Michigan and New Jersey who had two or more live births between 1989 and 2003. This allowed them to compare sibling infants and same mother's different pregnancies. Premature or delayed-birth infants were excluded, as were babies with extremely low or high birthweights, and mothers with diabetes.

In total, 513,501 women and 1,164,750 babies were included in the analysis.

On average, women gained 30 pounds during their pregnancies with 12 per cent gaining more than 44 pounds.

Heavy babies weighing 8.8lb or more accounted for 12 per cent of all births.

Compared with those putting on just 18lb to 22lb, expectant mothers gaining 44lb to 49lb were 1.7 times more likely to have a high birthweight baby. For those gaining more than 53lb, the chances more than doubled.

Comparisons between newborn infants and their brothers and sisters allowed genetic factors to be taken into account.