Pregnant mothers are being warned that the likelihood of their child being overweight in later life can be influenced by factors determined before they are born.
A first-born, premature or post-term child has an increased chance of being obese and developing diabetes later in life.
Professor Wayne Cutfield, director of the Liggins Institute at the University of Auckland, says obesity needs to be prevented earlier rather than being "inadequately addressed" later - and that includes debunking the cliche that it is okay for pregnant women to binge by "eating for two".
Professor Cutfield, who is speaking in Auckland at a transtasman obesity society meeting, said stronger education about healthy eating needs to be tailored to target women from their early teenage years.
He said a woman's health before pregnancy reflected on her child's health for the rest of its life.
Surprisingly, a recent study of the diets of women undergoing IVF treatments found few changed their alcohol, tobacco or coffee consumption prior to a successful pregnancy.
"If you look at the diets of women undergoing IVF, this is a highly motivated, educated group; if they're eating inappropriately what do we expect of the rest of the population?"
Professor Cutfield said it was a cliche that pregnant women could eat as much as they wanted to "because you're eating for two".
He said there were studies that proved the benefits of healthier diets for pregnant women but it was important that the information was more effectively taught.
The Australian and New Zealand Obesity Society's Annual Scientific Meeting will be held in Auckland from today until Saturday.
The theme of the three-day meeting is "for our children's children".