Does Baby’s Birth Weight Put Him at Higher Risk For Autism?

ByKylie McConville
May 2013
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New research, published in The American Journal of Psychiatry, has found " the first clear link" between babies who grow to above average size and birth and the risk of Autism Spectrum Disorder.

Following a study of more than 40,000 children’s health records in Sweden, a team of researchers from The University of Manchester, confirmed what earlier research concluded: that premature and poorly grown, low weight babies appear more susceptible to the condition.

Professor Kathryn Abel, from the University of Manchester’s Centre for Women’s Mental Health and Institute of Brain, Behaviour and Mental Health, who led the research said, “The processes that leads to Autism Spectrum Disorder (ASD) probably begin during fetal life; signs of the disorder can occur as early as three years of age. Fetal growth is influenced by genetic and non-genetic factors. A detailed understanding of how fetal growth is controlled and the ways in which it is associated with ASD are therefore important if we are to advance the search for cures.”

Researchers involved in the study believe that the Autism Spectrum Disorder has origins in both genetic and environmental causes. For the study, researchers looked at the data collected by the Stockholm Youth Cohort in Sweden, where early ultrasound data provides detailed weights of a baby’s progression in pregnancies. Following their birth, infants and children also take part in a structured clinical assessment of their social, language, motor and cognitive abilities.

The cohort contained records of 589,114 children ages 0-17 in Sweden between 2001 and 2007. Certain data was not necessary to the study and was removed: children too young for an ASD diagnosis, adopted children and non-Sweish or Stockholm residents, children not born in Sweden and twins. From the data that remained, researchers found 4,237 young people with autism and 36,588 children who did not have the condition. These children acted as the control group.

From the study, researchers found that bigger babies born weighing over 9 lbs. 14 oz. showed a higher incidence of autism, as did smaller infants born weighing less than 5.5 lbs. A baby who had poor fetal growth during pregnancy would have a 63% greater risk of developing autism compared to “normally” growing babies and a baby who was larger at birth would have a 60% greater risk than “normally” growing babies. This effect, researchers found, was independent of whether or not the baby was born pre- or post-term.

Abel said, “To our knowledge, this is the first large prospective population-based study to describe the association between the degree of deviance in fetal growth from the normal average in a population of children and risk of ASD with and without intellectual disability. We have shown for the first time categorically that abnormal fetal growth in both directions increases risk of autism spectrum disorder.” Adding that she and her team of researchers “think that this increase in risk associated with extreme abnormal growth of the fetus shows that something is going wrong during development, possibly with the function of the placenta.”

“Anything which encourages abnormalities of development and growth is likely to also affect development of the baby’s brain,” Abel said of the research, noting that the “risk appeared particularly high in those babies where they were growing poorly and continued in utero until after 40 weeks. This may be because these infants were exposed the longest to unhealthy conditions within the mother’s womb.”

But just because babies may grow in utero at different rates compared to “normally developing” fetuses, it does not mean they will be diagnosed with the Autism Spectrum Disorder. What the research finds is that these growth differences are linked with more instances of of the condition. More than anything, the research is intended to raise awareness and work closer to finding a cure than it is to label below or above average birth weight babies with the autism diagnosis. Abel is the first to recognize that because a link appears it does not rule out the need for further research to explain the how and why’s that so many parents and researchers have.

She said, “We now need more research into fetal growth, how it is controlled by the placenta and how this affects how the brain develops,” noting that one key place to start researching is, “maternal condition and healthy growth.”

Do you think baby’s birth weight could be a factor that leads to the ASD diagnosis?

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