It sounds like something out of a science fiction novel - people being programmed to develop obesity or diabetes 20 or 30 years before they are born, when they exist as a mere dot in their grandmother's womb.

But Perth researchers in a new field of medicine say the origins of many common diseases can be traced back far earlier than we could have imagined, even before we began life as a foetus a few centimetres long.

Their radical thinking is based on mounting evidence that lifestyle alone cannot be blamed for the blowout in chronic health conditions plaguing the modern world, and that the unborn child is programmed in a process known as epigenetics, which involves "ghost" messages passed from one generation to the next.

This brave new world linking genetics, pregnancy and the environment, broadly known under the research speciality area of developmental origins of health and disease, is in the international spotlight next week when some of the world's best scientific minds meet in Perth.

Congress director John Newnham, who heads the University of WA's school of women's and infants' health and the Women and Infants Research Foundation, said it was critical research, given the epidemic of obesity and type 2 diabetes that was fuelling more kidney failure, heart disease and blindness.

He said unborn babies were programmed for the environment their mother lived in and based on her levels of nutrition and exercise. If they were programmed for a world where there was plenty of food, the internal systems to protect them from hard times actually worked against them, making them more prone to overeating, obesity and diabetes.

But their conditioning started even before that because this programming was passed through several generations, affecting appetite, how much people ate and their tendency to put on fat.

"By the time of our birth, or soon after, much of our future is already determined, yet much of our research is focused at later times in life," according to Professor Newnham.

"The egg from which we have come developed in our grandmother's uterus because our mother had her full number of eggs at the time she was born. Messages are passed from one generation to the next, not just through our genes but from signals that sit on top of the genes and turn particular genes on or off."

Professor Newnham said diseases other than obesity had their origins earlier than previously thought. Susceptibility to breast and prostate cancers might increase with exposure before birth to chemicals that mimicked the effects of oestrogen.

There was a growing area of research looking specifically at the links between chemical exposures before birth and subsequent illness such as cancer. "We're pioneering a new field of medicine which is developing at a rapid pace and our understanding about how many chronic adult conditions such as obesity and diabetes arise early in life is an accelerating story," Professor Newnham said.

The related conference Epigenetics 2007, which will apply the theory of genes linked to the environment to not only human diseases but also to veterinary science and agriculture, is also being held next week.

Conference convenor Professor David Ravine, from the WA Institute for Medical Research, said the forces that shaped the development of the early embryo and stemcells were epigenetic switches and some master epigenetic switches were sensitive to the environment.

- Professor Ravine will give a free public lecture on epigenetics at 5pm on Monday at the Perth Convention Exhibition Centre. To register, phone 9389 1488.