The health of a mother before she conceives affects the chances of the child becoming obese later in life, British researchers say.
A study by the University of Southampton suggests having a greater number of early life 'risk factors' is a strong predictor of being overweight or obese in childhood.
Scientists from the university's Medical Research Council Lifecourse Epidemiology Unit looked at five early life risk factors: a short duration of breastfeeding (less than one month) and four maternal factors during pregnancy - obesity, excess pregnancy weight gain, smoking and low vitamin D status.
Published in The American Journal of Clinical Nutrition, the research shows at age four, children with four or five of the factors were 3.99 times more likely to be overweight or obese than children who had experienced none.
Fat mass was, on average, 19 per cent higher.
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."