Small and large birth weight linked to genetics of mother and baby – except in smaller babies

Maternal and baby genetics contribute to most cases where babies are born very large or very small, new research shows.

A large-scale study, conducted by the University of Exeter and Cardiff University, found the strongest evidence to date that genetics play a major role in most cases when full-term babies are born. in the top or bottom 10% of the weight spectrum.

However, in the three percent of babies with the lowest birth weight, genetics seem to play a less important role. This indicates that other factors may contribute to the short stature of babies. Research looked at 190 common genetic variations known to affect birth weight, but it’s possible that rare genetic changes in the baby will reduce growth in the smallest three percent. Other important factors could include the health of the mother or the fetus or the placenta, which transfers nutrients and oxygen to the baby.

The study was a collaboration also involving the 90s children of the University of Bristol, Imperial College London and the University of Oulu in Finland. The research was supported by the Wellcome Trust and the European Commission’s H2020 program.

Babies’ birth weight is important because babies born in extremity are at higher risk for complications. Smaller babies are more likely to be admitted to neonatal units and have a higher risk of death, while larger babies are at greater risk for complications during birth.

To examine how much birth weight was related to the genetics of mothers and babies, the team created a genetic score for higher birth weight. Posted today in PLOS Genetics, the study tested whether the genetic score was higher or lower in babies born very large or very small in a sample of nearly 12,000 babies and more than 5,000 mothers of European descent. Mothers and babies were from Children of the 90s, a health study based at the University of Bristol, the Exeter Family Study of Childhood Health, and the Northern Finland birth cohorts of 1966 and 1986.

Dr Robin Beaumont of the University of Exeter School of Medicine was the lead author of the study. He said: “This research sheds new light on why some babies are born very large or small. This knowledge will help parents and clinicians understand where to focus their medical care. Genetics played a lesser role in the three percent of babies with the lowest weight, suggesting that other factors such as placental health may have influenced their weight. “

Co-lead author and clinician Professor Sailesh Kotecha, Cardiff University, added: ‘It is important to identify the reasons babies are born with low birth weight because they are at risk. increased health problems later in life, including diabetes and high blood pressure. Our work shows that genetics is a key part of why some babies are born small, and raises the possibility that genetics could be used alongside maternal and placental factors to identify those who are most likely not to have reached. their growth potential. “

Professor Rachel Freathy, University of Exeter, who supervised the study, said: “Our study provides the best insight to date into how common genetic variations between people influence extremes in weight to the birth. We now need to better understand whether genetics or environmental factors are more important in subsequent health risks. “

The article is titled “Common Maternal and Fetal Genetic Variants Show Expected Polygenic Effects on Risk of Small or Large for Gestational Age (SGA or LGA), Except in the Smallest 3% of Babies”, and is published in PLOS Genetics.