By Margarita Nahapetyan
A new U.S. study examined children who were born more than three months before a due date and provided fresh evidence, linking pre-term birth and autism.
The study included nearly 1,000 children born very prematurely, at least three months before their due date, between 2002 and 2004. When the children reached 2 years of age, they were evaluated for early signs of Autism Spectrum Disorder (ASD), using a screening tool known as the Modified Checklist for Autism in Toddlers (M-CHAT). This tool flags children who may have autism but is not considered to be a definitive diagnosis.
Dr. Karl Kuban, M.D. of Boston University School of Medicine and Boston Medical Center, who led the study, said that children born at least three months prematurely commonly suffer from motor, hearing or vision impairments, therefore increasing their chances of testing positive on the M-CHAT screening. So, in order to have a better picture of the risk for developing autism in children born too early, the researchers took out the children with pre-existing impairments and screened the remaining children with the M-CHAT checklist.
The odds of M-CHAT positive findings associated with the disabilities were: 23-fold higher for those who could not sit or stand without help compared with those who could walk; more than 7 times higher for those who needed assistance to walk compared with those who could walk; 4 to 13-fold higher for children with cerebral palsy depending on their condition; 8.4 times higher for children considered blind and those with a hearing impairment; 13-fold higher for children with a Mental Development Index score below 55 and more than 4-fold for those with a score of 55 to 69 compared with those who had score of 70 or higher.
Even after taking these children with pre-existing conditions out, 16 per cent of the children scored positive for possible autism. After also excluding children with cognitive impairment on the premise that it may not be autism related, about 10 per cent of the pre-term children still had a positive screening score. However, many of the items on the test, such as avoidance of eye contact, inconsistent response to voice, and failure to show toys or play with them, require the child to have intact motor, visual, and hearing abilities, while an extremely early birth increases the risk of these systems.
Dr. Kuban warned that the test was not conclusive in determining whether a child will develop autism. "You have to acknowledge that a positive screen is not the equivalent of autism," he said and added that his study may also be seen as an indication that the evaluation is far more prone to a false positive -- in essence, indicating that a child has autism when he or she does not -- than many might believe. What the test could actually do is provide doctors and parents with useful information when it comes to premature children, cautioning them that they might be at greater risk of being diagnosed with autism later on in life."The studies don't prove that extreme prematurity is directly linked to autism because the children who participated were too young to have a confirmed diagnosis, Dr. Kuban said, "We should know more in a few years if we are able to follow these children."
Dr. Neil Marlow and Dr. Samantha Johnson of University College London pointed in their related editorial that because early identification leads to early treatment of children with Autism Spectrum Disorders, screening tests are designed to over-identify children at risk. They suggest that useful knowledge may be obtained by following the children as they grow up to determine how many of those who initially screened positive actually develop the disorder. Dr. Marlow notes that the study is valuable because "it raises our awareness of the difficulties in interpreting screening results." He warns that further study is needed before conclusions can be drawn about the direct connection between premature birth and ASD.
Autism refers to a group of developmental problems, known as Autism Spectrum Disorders. It appears in early childhood and is characterized by difficulty with social interaction, problems with all forms of communication and repetitive behaviors or obsessive interests. Depending on each individual case, the severity of these behaviors can range from mild to disabling. While many experts say that autism can be caused by genetic and environmental factors alike, it still remains unclear which factor plays a bigger role in the onset of the disorder.
The Centers for Disease Control and Prevention (CDC) estimates that between two and six per 1,000 children have an Autism Spectrum Disorder, or somewhere between one in 500 to one in 150. The risk is three to four times higher in males than females.