Medical experts have long linked cancer risk with their genes and lifestyles as adults.
But Professor Rocardo Uauy claims that factors of a mother's life such as whether she smokes, drinks, or is overweight all play key roles.
It is believed that environmental factors that encourage obesity and weight-gain in children can increase their risk of getting cancer, reports the Daily Mail.
"Someone's risk of developing cancer starts from before the time of conception. The risk factors are already operating in the mother's eggs before conception," said Uauy in The Observer newspaper.
"Yes, cancer is a genetic disease, but your chances of getting cancer are affected by the environment in which you live. So it's not just about if you smoked from the age of 12."
"But did your mother smoke? What was the water like that she drank? Is she exposed to toxins such as dioxins, which are found in the environment, and did she pass them on to her baby through her breast milk?"
Uauy has been a leading advisor to the United Nations and the World Heath Organisation for several years and is believed to have compiled one of the most detailed pictures of cancer prevention yet.
He recommends that parents reduce their baby's cancer risk by eating less tinned food and reducing exposure to certain cancer-causing chemicals.
Women should stop smoking before they conceive as cigarettes can increase the risk of children having a low birth weight.
Research suggests that underweight children put on weight quickly around their middles in early years which adds to the risk of cancer later on.
He added: "Mothers-to-be only need to consume an extra 150 calories a day during the nine months of pregnancy and should not eat for two."
Uauy recently highlighted the growing evidence of how early-life factors affect cancer risk at a World Cancer Research Fund conference.