Optimal birth weight may help reduce risk of mental health problems in children

New research from the University of Medicine and Health Sciences RCSI has found that babies with higher birth weights tend to have fewer mental health and behavioral problems during childhood and later life. adolescence.

These results could help identify and support the children most at risk of developing psychological problems.

The study, published in European child and adolescent psychiatry, examined birth weight and subsequent mental health in thousands of children in Ireland. Unlike many studies looking at birth weight, it used data that followed the same children repeatedly through their childhood and adolescence using the Growing Up in Ireland study, an ongoing government-funded study of children born between 1997 and 1998.

The analysis showed that each kilogram below average birth weight (3.5 kg or 7 lb 11 oz) was associated with more reported mental health problems throughout childhood and adolescence. The study also found that these birth weight issues tend to persist throughout childhood, from ages 9 to 17. The types of problems most strongly linked to birth weight were inattention, impulsivity and hyperactivity, behaviors commonly associated with attention deficit hyperactivity disorder (ADHD). Each drop of one kilogram below average birth weight was associated with a 2% increased risk of ADHD-like behaviors, but these behaviors were within the normal range. That is, even in very low birth weight infants (1.5 kg), the average number of ADHD symptoms would probably not reach the threshold for an ADHD diagnosis.

Low birth weight was also linked to emotional and social problems, particularly in late adolescence. These problems were found to be more severe and closer to clinical thresholds, for example for the diagnosis of depression or anxiety.

We have known for many years that low birth weight and premature birth are linked to a higher risk of mental illness in children. What this study shows is that even small deviations from typical birth weight could also be relevant.”

Professor Mary Cannon, RSCI Professor of Psychiatric Epidemiology and Youth Mental Health and Principal Investigator

Niamh Dooley, PhD student and lead author of the study, said. “This relationship between birth weight and child mental health persists even after accounting for factors that might influence both birth weight and mental health, such as gender, socio-economic factors, economic and parental history of mental illness.The effect of birth weight on later mental health is likely small, but this could interact with other risks such as genetics and childhood stress, and have implications for understanding the origins of mental health and ill health.

This study shows the importance of good perinatal care and suggests that improving the overall health of women during pregnancy to ensure optimal birth weight can help reduce the risk of offspring developing mental health problems. Children with low birth weight may benefit from psychological assessments during childhood and early intervention for mental health symptoms if detected to help minimize the burden of mental illness later in life. adolescence and into adulthood.

Other research from the group has just been published in Research on child and adolescent psychopathology. It indicates that a significant percentage of the association between birth weight and ADHD symptoms in Irish children can be explained by maternal substance use during pregnancy (smoking, alcohol use, drug use without a prescription).

This research was supported by a StAR International PhD Fellowship awarded to Niamh Dooley and funding from the Health Research Board and the Irish Research Council. Funding for open access was provided by the IReL consortium. Professor Cannon is funded by a European Research Council Consolidator Award.


RCSI University of Medicine and Health Sciences

Journal reference:

Dooley, N. et al. (2022) The persistent effects of fetal growth on the mental health of children and adolescents: longitudinal evidence from a large population-based cohort. European child and adolescent psychiatry. doi.org/10.1007/s00787-022-02045-z.


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