The largest genetic study of its kind has led to new insights into how the genes of mothers and babies influence birth weight.
University of Queensland scientists helped identify 190 links between the genetic code and birth weight, two-thirds discovered for the first time.
It is the result of a large-scale international collaboration, led by UQ and the Universities of Exeter, Oxford and Cambridge.
UQ Diamantina Institute researcher Dr Nicole Warrington said birth weight was an essential determinant of infant health.
"A low birth weight can not only put the baby at risk of mortality, but it is also associated with increased risk of developing diseases such as Type 2 diabetes and high blood pressure when the baby grows up," Dr Warrington said.
Research found the direct effects of the baby's genes made a substantial contribution to birth weight.
However, around one-quarter of the genetic effects identified were from the mother's genes.
The mother's genes affected the baby's growth by influencing factors in the baby's intrauterine environment during pregnancy, such as the amount of glucose that is available to influence their growth.
UQDI Statistical Geneticist Professor David Evans said it was the first time these genetic effects could be teased apart.
"This is the first time we've really been able to unpick the effects of both the mother's and the baby's genes on birth weight," Professor Evans said.
"It is particularly useful to know about the maternal genetic influences on the intrauterine environment because the identity of these genes gives us clues as to which factors, such as glucose, causally influence fetal growth.
"Better understanding of the causes may mean we can help ensure babies are born at healthy weights."
The study also investigated the relationship between birth weight and diseases in later life.
"The methods we have developed to disentangle maternal and fetal genetic influences on birth weight have real potential to tell us also about the effects of the intrauterine environment on later-life outcomes in the child," Dr Warrington said.
"For example, smaller babies are more likely to have higher blood pressure in adulthood.
"Our work shows that this is due to genetic effects; we found no evidence that adverse intrauterine environments can raise your blood pressure in later-life."
The research is published in Nature Genetics (DOI: 10.1038/s41588-019-0403-1).