Birthweight is one of epidemiology’s most accessible and misunderstood variables. The weight of a baby at birth is strongly related to the risk of mortality during the first year and, to a lesser extent, to developmental problems in childhood and the risk of various diseases in adulthood.
According to new research from RCSI University of Medicine and Health Sciences, babies with higher birth weights have fewer mental health and behavioral issues in childhood and adolescence. These findings may aid in identifying and supporting children who are at a higher risk of developing psychological problems.
The study, published in the journal European Child & Adolescent Psychiatry, looked at birth weights and subsequent mental health in thousands of Irish children. Unlike many birth weight studies, it used data from the Growing Up in Ireland study, an ongoing government-funded study of children born between 1997 and 1998, to follow the same children throughout their childhood and adolescence.
The study found that every kilogram under the average birth weight (3.5kg, or 7lbs 11oz) was associated with more reported mental health problems during childhood and adolescence. The study also discovered that these birth-weight-related issues tend to persist throughout childhood, from the ages of 9 to 17.
For many years, we have known that low birth weight and premature birth are associated with an increased risk of mental illness in children. This study demonstrates that even minor deviations from the average birth weight may be significant.
Professor Mary Cannon
The type of problems most strongly linked with birth weight were inattention, impulsivity and hyperactivity, behaviours generally associated with Attention Deficit Hyperactivity Disorder (ADHD). Each kilogram drop below the average birth weight was linked with a 2% increase in risk of ADHD-like behaviours, however such behaviours were within the normal range. That is, even among children with very low birth weights (1.5kg), the average number of ADHD symptoms would probably not meet the threshold for an ADHD diagnosis.
Lower birth weight was also linked to emotional and social problems, especially in late adolescence. These issues were discovered to be more severe and closer to clinical thresholds, such as those for diagnosing depression or anxiety.
Professor Mary Cannon, RSCI Professor of Psychiatric Epidemiology and Youth Mental Health and the study’s Principal Investigator, stated: “For many years, we have known that low birth weight and premature birth are associated with an increased risk of mental illness in children. This study demonstrates that even minor deviations from the average birth weight may be significant.”
Niamh Dooley, PhD student and study lead author, stated. “Even after accounting for factors that could influence both birth weight and mental health, such as gender, socioeconomic factors, and parental history of mental illness, the relationship between birth weight and child mental health persists. Although the effect of birth weight on later mental health is likely small, it may interact with other risks such as genetics and childhood stress, which could have implications for understanding the origins of mental health and ill-health.”
This study emphasizes the importance of good perinatal care and suggests that improving women’s overall health during pregnancy to ensure optimal birth weight may help reduce the risk of their children developing mental health problems. Children with low birth weight may benefit from psychological assessments in childhood, as well as early intervention for mental health symptoms if they are detected, in order to reduce the burden of mental illness later in adolescence and adulthood.
The group’s latest findings have just been published in the journal Research on Child and Adolescent Psychopathology. It suggests that maternal substance use during pregnancy can explain a significant portion of the association between birth weight and ADHD symptoms in Irish children (smoking, alcohol-use, non-prescription drug-use).
