By age six, the risk increased so that these children were 4.65 times more likely to be overweight or obese and fat mass was 47 per cent higher.
Importantly, these differences were not explained by other factors, such as the children's quality of diet or physical activity levels.
The data analysed came from 991 children taking part in the Southampton Women's Survey - one of the largest studies of mothers recruited before pregnancy, along with their infants and children.
Professor Sian Robinson, who led the study, said: "Early life may be a 'critical period' when appetite and regulation of energy balance are programmed, which has lifelong consequences for the risk of gaining excess weight.
"Although the importance of early prevention is recognised, much of the focus is on school-aged children.
"Our findings suggest interventions to prevent obesity need to start earlier, even before conception, and that having a healthy body weight and not smoking at this time could be key."
- PAA