High Rate of Autism Signs In Ex-Preterm Infants

Premature infants born less than 1500 grams have an increased risk for showing early signs of autism according to a study conducted at Children's Hospital Boston. The findings, published in the April issue of Pediatrics, suggest that early autistic behaviors appear to be an under-recognized feature of infants born with a very low birth weight and that early screening for signs of autism may be warranted in preterm infants.

"Extremely premature infants are known to have a high prevalence of learning disabilities, attention and behavioral problems," says Catherine Limperopoulos, PhD, research associate in the Department of Neurology at Children's and lead author on the paper. "Our findings suggest that early screening tests for autistic features might be warranted in this population. Should these children test positive on autism screening tests, follow-up specific diagnostic testing for autistic spectrum disorders should be performed."

The longitudinal study followed 91 preterm infants who weighed less than 1500 grams (3.3 lbs) at birth. The infants underwent conventional MRI studies prior to discharge from the neonatal intensive care unit. Pertinent demographic, prenatal, intrapartum, and short-term outcome data were then collected and follow-up assessments were performed on all of the infants at 22 months. The results of the study found that 25% of the children assessed tested positive on an autism screen test.

Autism affects 1 in 150 children worldwide, and is the fastest growing developmental disorder in the world. Recent advances in the field of early detection have facilitated the early and accurate screening of infants so as to prompt appropriate referrals for specialized testing.

Three well validated assessments were used to conduct follow-up testing of each ex-preterm infant; the Modified Checklist for Autism in Toddlers (M-CHAT), a parent report checklist is a screening tool for early autistic features, assessing sensory responsiveness, early language and communication, social relatedness and early joint attention; the Child Behavior Checklist, a questionnaire for caregivers that examines internal (withdrawal, emotionally reactive, anxiety) and external (attention deficit, aggression) behaviors in young children; and the Vineland Adaptive Behavior Scale, a measure of functional abilities in motor, communication, socialization and daily living skills.

Since developmental delays are already common among preterm babies, the authors controlled for motor and language delays in their analyses in order to account for any confounding effects. The increased rate of positive testing on autism screening tests persisted after controlling for these potential confounders. Infants who tested positive on the M-CHAT were also found to have internalizing behavioral problems on the Child Behavior Checklist and socialization and communication deficits on the Vineland Adaptive Behavior Scale.

Several risk factors associated with a greater likelihood for positive M-CHAT were identified. These included the presence of maternal infection and acute intrapartum bleeding, the baby's illness severity score after birth, low birth weight and gestational age, prenatal infection, and abnormal MRI studies. Higher positive autism screenings among males were also seen which corroborates previous studies reporting a significant association between autism spectrum disorders and the male gender.

While the findings are significant, the researchers are quick to remind the public that the study used an autism screening test to identify toddlers at risk, and a positive autism screen does not diagnose autism spectrum disorders, but identifies infants that should undergo definitive diagnostic autism tests.

"This research was done in a selected high-risk population of very preterm infants and by no means are we suggesting all premature babies are at risk for autism," adds Limperopoulos, who is also an assistant professor in the department neurology and neurosurgery at McGill University. "It is still unclear whether these initial findings are transient or whether these findings will persist in these children as they grow older."