The findings, published in The American Journal of Psychiatry, show the first clear link between large babies at birth and the risk of Autism Spectrum Disorder.
The study was led by researchers from the University of Manchester, England, and supports prior research that suggests that premature and poorly grown, low weight infants are at a higher risk for the disorder.
A study by Northwestern University conducted last year suggested that birth weight is an environmental factor contributing to the risk of autism
Autism is a condition that influences how people communicate with others, and there is no known cure. According to the CDC (Centers for Disease Control and Prevention), 1 in every 50 kids in the USA has an autism spectrum disorder. Approximately 1% of all children in the UK have this disorder, according to NHS (National Health Service) figures. Researchers think it is a consequence of environmental and genetic factors.
Professor Kathryn Abel, from the University's Centre for Women's Mental Health and Institute of Brain, Behaviour and Mental Health, and lead researcher explained:
"The processes that leads to 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.
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."
The investigators examined data from the Stockholm Youth Cohort in Sweden, where early ultrasound data provide detailed weights of the baby's development in pregnancy. Children and babies also participate in clinical analyses of their motor, language, social, and cognitive skills.
The cohort included records of 589,114 kids aged 0 to 17 years in Sweden between 2001 and 2007. The researchers eliminated data that consisted of children too young to have an ASD, adopted kids, non Swedish or Stockholm County residents, children not born in Sweden, as well as twins.
With the available left over data, the investigators found 4,283 young people with autism and 36,588 without autism who acted as controls.
Study results showed that among the larger babies, i.e. those who were born weighing more than 4.5kg (9 lbs. 14 oz), autism prevalence was higher - the same pattern was seen in smaller infants who were born weighing less than 2.5kg (5.5 lbs.).
The authors found that:
- Babies with poor fetal growth (very light babies at birth) were 63% more likely to be diagnosed with an ASD later on
- Very large newborns were 60% more likely to be diagnosed later on with an ASD
"We 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. 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."
The authors suggest further research be conducted on fetal growth and how it is controlled by the placenta, and how this impacts development of the brain.
They pointed out that the current study was also one of a kind, because it examined the differences between kids who developed ASD with and those without intellectual disability in addition to children born before and after the 40 week mark.
A study released last week by the Yale School of Medicine suggested that a newborn's placenta can predict his or her risk for autism. Placentas with abnormal folds or cell growths can increase the risk for autism.
Written by Kelly Fitzgerald