Born to be fat?

Expectant mothers who watch their weight during pregnancy increase the chances their baby will maintain a healthy weight throughout life, according to a study in the British journal The Lancet.

But when pregnant women overindulge and gain too much weight during their 9 months, they tend to give birth to heavier babies who are at higher risk for obesity as children and adults, the researchers found.

Obesity is associated with a number of health issues including cancer, heart disease, type 2 diabetes and asthma.

Study author Dr. David Ludwig of Children's Hospital Boston set out to  determine if pregnancy weight gain alone is related to higher infant birth weights and not due to obesity-related genes.

Ludwig and his colleagues reviewed medical records of more than one and a half  million women and children over a 15 year period.  Each woman had 2 or more children. The researchers examined the differences in the amount of weight gained by the same mom in each pregnancy to see if these differences affected the weight of each child.

"A woman who gained 50 pounds during pregnancy compared to 20 pounds had double the risk of having a high birth weight baby," said Ludwig.

The babies born to heavier mothers weighed at least 8 and a half pounds, or a third of a pound more than the children of mothers who weighed less.

Scientists are still trying to determine how excess pregnancy weight leads to weight gain down the road for children,

Ludwig speculates some of a mother's excess calories make their way across the placenta not only making the baby heavy but disrupting some key stages of the child's development. Extra sugar, called glucose, and other factors affect the infant's genes and "may produce permanent changes in the baby's tissues or in the brain regions that regulate hunger and metabolism," he said.

This means these children tend to want to eat more, and may gain more weight than other children even when eating the same amount of food.

Ludwig and other experts have said that the childhood obesity epidemic in the United States may shorten life expectancies for the first time since the Civil War unless something is done about it.

"Because birth weight influences lifetime risk of chronic illness and especially obesity, the best time to begin obesity prevention efforts for the next generation may be before birth," explains Ludwig.

Last year the Institute of Medicine released new guidelines for healthy weight gain during pregnancy. Women should gain 28 to 40 pounds if underweight, 25 to 35 pounds if they are at a normal weight, 15 to 25 pounds if they are overweight, and 11 to 20 pounds if they are obese.