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Birth Size Link to Teen Mental Health Conditions

A child’s birth weight and length can partially predict the likelihood of being diagnosed with mental health conditions such as autism and schizophrenia later in life.

Dr Sean Byars of The University of Melbourne analysed the medical records of 1.75 million Danish births and found that genetic imprints established at conception could influence both size at birth and mental health during childhood and adolescence. The findings are consistent with evolutionary theory, which predicts that disruptions to specialised genes may have effects on foetal growth and neurodevelopment.

Birth size was used to capture the later risk of autism and schizophrenia. Very small babies had increased risks for most mental disorders.

“We found that heavier and longer babies had enhanced risk for autism and reduced risk for schizophrenia, while the opposite held for lighter and shorter babies,” Byars said. “For example, Danish newborns are on average 52 cm long, and being born at 54 cm increases the autism risk by 20%. However, these are relative risks and these disorders remain rare,” he said.

“Risk patterns are opposite in smaller newborns, who have higher risk for schizophrenia and lower risks for autism,” he said.

Byars, who conducted the study while at the Copenhagen Centre for Social Evolution, said the findings will contribute to a more comprehensive understanding of the factors that make people vulnerable to such conditions.