New research shows a link between babies born to term with a weight lower than 3.5kg and a higher risk of neurodevelopmental disorders.
Neurodevelopmental disorders are brain disorders that affect an individual’s ability to think, learn, make decisions, and interact with others. Neurodevelopmental disorders include autism, cerebral palsy, and intellectual disability. These disorders often become apparent during childhood or adolescence with some symptoms going unnoticed until later in life.
The research, carried out by the University of Bergen, analysed whether there was a relationship between lower birth weight and neurodevelopmental disorders.
Neurodevelopmental disorders
Historically in the medical industry, it is well-known that being born preterm leads to a higher risk of health issues later in life, including neurodevelopmental disorders such as ADHD and autism. However, most babies that develop neurodevelopmental disorders are born to term.
Marianna Cortese at the Department of Clinical Medicine wanted to discover if being born at term but with a lower weight, affected the risk of developing neurodevelopmental disorders.
The research team used data from the Medical Birth Registry in Norway and analysed 1.8 million births. By using the unique personal identifiers assigned at birth, they linked the data to other mandatory health and administrative registries. This method meant that the researchers could follow the babies’ health into adulthood.
Scientists adjusted for influential factors such as maternal smoking, marital status of the mother, and immigrant status. However, those factors had a trivial impact on the result.
“Compared to babies born with a weight in the range of 3.5-3.9 kg, lower birth weight was associated with an increased likelihood of developing one of the above neurodevelopmental disorders. We conclude that lower birth weight can be a marker of neurodevelopmental (ND) disabilities independent of preterm delivery,” said Cortese.
Strong associations discovered
The strongest association was found for cerebral palsy, with 25-fold increased odds for the lowest birth weights. Following this, a 16-fold increase for vision/hearing disabilities, 11-fold for intellectual impairment and 7-fold for schizophrenia. Furthermore, 5.4-fold was present for epilepsy and 3.5-fold for behavioural disorders such as ADHD.
Cortese added: “Despite these large associations and risk increases, low birth weight only explains a smaller proportion of term ND disabilities (the largest proportion was for intellectual disability with 21%), meaning that these are complex multifactorial diseases”.
The research team excluded data of babies with malformations from the study.
“Malformations can be part of syndromes and are associated with neurodevelopmental disorders. Therefore, we excluded babies with malformations to minimise the possibility that our results could be due to babies with malformations,” noted Cortese.
The only risk factor that the team adjusted for, that made an impact on the result, was the year of birth. “Year of birth could be capturing trends that are going on related to other risk factors, the occurrence of ND disorders, changes in care, et cetera,” Cortese explained.
Is low birth weight an independent risk factor?
Despite the strong relationship between low birth weight and neurodevelopmental disorders, the researchers stated they do not think that low birth weight is an independent risk factor.
“We believe that lower birth weight indicates that something may have happened during the pregnancy that led to slower growth and consequently to lower birth weight, and this event predisposes or increases at the same time the risk of certain ND disabilities. Low birth weight could thus be a marker of some prenatal insult or problem,” she said.
Furthermore, babies born with a higher birth weight than normal also have an increased risk for the same disabilities. As to what are the potential clinical outcomes of this study, Cortese concluded: “Hopefully these findings will motivate further research on potential prenatal insults, events, problems, pathologies that could be the underlying cause of some ND disabilities.
“If these are causes that could be intervened on that means we one day maybe would be able to prevent the occurrence of ND disabilities in some children.”
