Is a Big Baby More Likely to Have Autism?

Your baby's birth weight and length could predict whether he'll be diagnosed with autism or schizophrenia later in life, according to one study.

Your baby's birth weight and length could predict whether he'll be diagnosed with autism or schizophrenia later in life, according to a new study conducted by the University of Copenhagen and Yale University.

Researchers there found that big babies are more likely to develop autism but are at lower risk of schizophrenia. Conversely, smaller babies are more likely to be diagnosed with schizophrenia but are at a lower risk of becoming autistic. To reach these conclusions, scientists examined medical records of some 1.75 million Danish births and subsequent hospital diagnoses for up to 30 years, according to an article in The Independent. The findings were published this week in the journal Proceedings of the Royal Society, London B.

But before you start fretting over your kiddo's extra pound or half-inch, keep in mind that autism and schizophrenia are relatively uncommon and the increased risk we're talking about is fairly small. In an example from the study, the average Danish newborn is 52 cm (or 20.4 inches). If a baby is born 2 cm longer, his chances of becoming autistic increase by 20 percent. Or, put another (less scary) way, his absolute risk bumps up from 0.65 percent to 0.78 percent.

Researchers believe "genomic imprinting" could at least partially explain the link between birth size and mental health disorders. According to this evolutionary theory, while baby is in utero, some genes inherited by the father are expressed differently to ones inherited by mom. In most pregnancies, the opposing genes balance each other, resulting in an average-sized baby with a "high likelihood of balanced mental health development," reports Science Daily. But as researchers discovered, when there's a larger imprinting imbalance, the baby is at a higher risk of autism or schizophrenic.

"It's quite likely that these imprints that cause either heavier babies or lighter babies are doing parallel things to the infant brain as it grows up," said Professor Jacobus Boomsma, director of the Centre for Social Evolution at the University of Copenhagen. "Exactly how that works mechanically on a genomic level we have no idea, but that is what the theory predicted and what the evidence here supports."

Boomsma said more research is needed to figure out which genes are involved and how, exactly, they affect baby's brain. Still, these and other recent findings can only help us parents. Besides offering some clues about the origin and nature of the disorder -- and helping us separate fact from fiction -- they can illuminate ways we can best support our children.

Tell us: What do you make of this study?

A simple test developed by the Kennedy Krieger Institute in Baltimore may be able to help determine whether a child will develop autism and other forms of developmental delays. The pull-to-sit test, done in infants as young as six months old, monitors whether or not a child has head lag, or trouble controlling his neck and head. While the test is not a diagnosis, children with head lag have a higher risk of autism or other social or communication delays.

Image of newborn courtesy of Shutterstock 

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