A new study reports that babies whose growth in the womb is at either end of the extreme — either very small or very large — are at a greater risk of developing autism.
According to researchers at The University of Manchester in the U.K., the new study shows a clear link between babies who grow to above average size in utero and the risk of autism spectrum disorder (ASD).
The new study also confirms earlier research that showed premature and low weight babies appear more susceptible to autism.
“The processes that leads to ASD probably begin during fetal life,” said Professor Kathryn Abel, from the University’s Centre for Women’s Mental Health and Institute of Brain, Behavior and Mental Health, who led the research.
“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.”
The U.K. researchers looked at data from the Stockholm Youth Cohort in Sweden, where early ultrasound dating provides detailed weights of babies’ progression in pregnancy. Infants and children then take part in structured clinical assessments of their social, motor, language and cognitive abilities.
The data contained records of 589,114 children up to the age of 17 between 2001 and 2007. Certain data was removed, including children too young to have a diagnosis for ASD, adopted children, children not born in Sweden, and twins.
In the remaining available data, researchers found 4,283 children with autism and 36,588 who did not have it and who acted as the control group.
The study found that bigger babies who were born weighing over 4.5kg (or 9 pounds, 14 ounces) showed a higher incidence of autism, as did smaller infants who were born weighing less than 2.5kg (5.5 pounds).
A baby who had poor fetal growth would have a 63% greater risk of developing autism compared to normally grown babies, the researchers report.
A baby who was large at birth would have a 60% greater risk. This effect was independent of whether or not the baby was born prematurely, the researchers noted.
“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,” Abel said.
Anything that encourages abnormalities of development and growth is also likely to affect brain development, she added.
“Risk appeared particularly high in those babies where they were growing poorly and continued in utero until after 40 weeks,” she noted. “This may be because these infants were exposed the longest to unhealthy conditions within the mother’s womb.”
The researcher said more research into fetal growth is needed, specifically looking at how it is controlled by the placenta and how it affects brain development.
“One of the key areas to research is maternal condition and healthy growth,” she said.
The research was published in The American Journal of Psychiatry.
Source: The University of Manchester