A father's genetic code influences the weight of a baby at birth, according to a new study.

The study led by the UCL Institute of Child Health (ICH) suggests that genes inherited from the mother and father regulate a baby's growth at different times during the pregnancy, to ensure a successful birth as well as the mother's survival.

Low birth weight is a well-known risk factor for Type 2 diabetes and cardiovascular problems in later life.

One group of growth genes of particular interest are the imprinted genes inherited from one's parents. If the paternal one is expressed, the maternal one is imprinted (silenced) and vice versa.

The 'parental conflict hypothesis' suggests that expression of the father's genes enhances a baby's growth, improving the success of the paternal genome to be passed on.

In contrast, the mother's genome limits foetal growth, distributing equal resources to each of her offspring, whilst ensuring her own survival post-birth allowing her to reproduce again.

The study, published in the journal PLOS ONE, looked at the relationship between birth weight and the paternally expressed Insulin-like growth factor 2 (IGF2) early in gestation, where IGF2 is a key hormone regulating growth in the womb.

Professor Gudrun Moore, lead author at the UCL Institute of Child Health, says most of us think of both the mother's and father's genes as having an equal influence on birth weight, but this does not appear to be the case.

"Our study suggests that the two parental genomes may be acting at different times during the pregnancy in order to control the baby's size. Whilst greater foetal growth appears to be promoted by the father's genes early on, it must still require careful regulation by the mother to ensure a successful birth," he said.

He added that understanding the genetic basis of foetal growth is of critical importance in the prevention and monitoring of small and low weight babies.