Skip to main content

How both mother and baby genes affect birth weight


The largest study of its kind has led to new insights into the complex relationships surrounding how mothers’ and babies’ genes influence birth weight. The research identifies 190 links between our genetic code and birth weight, two-thirds of which are identified for the first time.

The result of a largescale international collaboration, with more than 200 international researchers involved, has now been published in Nature Genetics. Responsible for some of the Swedish and the Norwegian parts of the study is Bo Jacobsson, Professor of Obstetrics and Gynecology at Sahlgrenska Academy, University of Gothenburg.

Scientists have known for long time that babies who are particularly small at birth have a higher risk of birth complications, and also tend to be more prone than average weight babies to high blood pressure in adulthood. To understand the relationships between birth weight and such risks to health, it is necessary to understand the contributions of both genetics and the environment. But until now, these have been unclear.

This study casts new light in this area by allowing scientists to clearly separate the effects of a mother’s genetics on birth weight from the baby’s own genetics for the first time.

Separated effects

The research studied the genetic information from 230,069 mothers, with the birth weight of one child each, in addition to genetic information and birth weights of 321,223 people across the Early Growth Genetics consortium cohorts and the UK Biobank. They used novel statistical methods to tease apart the effects of the mothers’ and babies’ genes on the weight of newborn babies.

The researchers concluded that the direct effects of a 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 that were not passed on to the child. Instead, these affected the baby’s growth by influencing factors in the baby’s environment during pregnancy, such as the amount of glucose available.

The study found that some parts of the genetic code can, both directly from the child and indirectly from the mother, be linked to birth weight. A number of these genetic effects were seen to work together, with the mother and baby pushing birth weight in the same direction, while others had opposing effects, like a mother-baby tug of war.

Important understanding

For example, some of the genetic effects that raise the mother’s glucose levels work to make the baby bigger because the baby produces more insulin in response which makes it grow. But when those same variations in the genetic code are inherited by the child, they restrict the amount of insulin the baby can produce, so limiting its growth and counter-acting some of the mother’s growth-promoting effects.

Understanding the factors that influence birth weight is important because babies who are born very large or small have lower chance of survival and higher later-life risk of metabolic diseases.

– There has been an influencing idea about low birth weight program the individual to get high blood pressure later in life. Now we can show that both low birth weight and high blood pressure later in life are effects of the same genetic coding, which is one of the most interesting results in the study, says Bo Jacobsson.

Title: Maternal and fetal genetic effects on birth weight and their relevance to cardio-metabolic risk factors

Contact: Bo Jacobsson

Images: Genre image (photo: Margareta G. Kubista) and portrait image of Bo Jacobsson (foto: Paulina Jacobsson)