A study has found that mothers-to-be who gain too much weight are more likely than others to have fatter children.
It is well established that larger mothers have heavier babies at birth, but previously factors like genes shared between mother and child were thought to explain weight problems as children grow up.
But a new study comparing sisters and brothers shows obesity in children can be attributed to the mother's weight during pregnancy.
The study claimed that by controlling an expectant mother's weight, preventative measures could be taken to avoid later health problems for her child.
"Since high birth weight increases risk for obesity and diseases such as cancer and asthma later in life, these findings have important implications," the Daily Express quoted co-author Dr David Ludwig, of Boston Children's Hospital in the US, as saying.
He and Professor Janet Currie, of Columbia University, monitored births in Michigan and New Jersey from 1989 to 2003.
The study has been published in the Lancet.