The BBC's John Maguire explains the birthweight breakthrough

The scientists have been conducting research into whether diabetes is passed on through the genes.

For three years, they have been looking into how the genes a baby inherits can affect the production of blood sugar and their birthweight.

They wanted to know what could cause two children born from the same mother to have very different birthweights.

The outcome of their research has been published in 'Nature Genetics' and is being celebrated as a major breakthrough.

Insulin

The research revealed a link between growth in the womb and genetic changes which affect the production of insulin.

Insulin controls blood sugar levels in adults. The quantity of insulin increases the more food people eat.

Dr Hattersley says insulin could explain baby growth

Dr Andrew Hattersley of Exeter Postgraduate Medical School said: "The crucial thing we have shown is that insulin is a key determinant in why a baby grows."

Previous research into baby birthweight has concentrated on what the mother eats and whether she smokes.

The new research throws the spotlight onto babies and their genetic make-up.

History of diabetes

Dr Hattersley said: "Everyone thinks baby brithweight is due to what the mother does, but we have shown that if a baby inherits a gene which affects its production of insulin, it is likely to be lighter.

"This helps us understand how babies grow in the womb."

Babies with low birthweight may go on to have problems with high blood pressure and diabetes.