By age 4 months, the affected children were more likely to have a visual preference for higher amounts of stimulation, much like newborns.
"Continuing higher attention to more stimulating events of infants with ASD at 4 months represents a lack of transition to more mature levels past the neonatal period, providing evidence for early atypical development, including the visual system," according to the researchers.
The "consequences of these very early sensory and motor signs may be an arrest in performance beginning as early as 7 to 10 months' postterm age such that cognitive and motor development as measured by standardized instruments is significantly slowed or suppressed," they wrote.
Indeed, the infants who were later diagnosed with an ASD had sharper declines in motor performance by 7 months and in mental performance by 10 months.
The authors acknowledged some limitations of the study, including the lack of investigation into social, communication, and language development, the small sample size, and the fact that not all children later determined to have an ASD received clinical diagnoses. The findings may therefore not be specific to all children with ASD and emphasize the need to replicate these retrospective findings with more directed prospective studies, they noted.
While autism is heterogeneous in cause, "our report helps to confirm a substantial prevalence of ASD in NICU graduates, making them important to study," the authors commented.
Whether the NICU graduates studied are typical of other ASD-affected infants who lack early medical issues is not clear, they added. "It also is not clear whether this group is emergent within the increasing cohort of surviving very tiny and preterm infants or identified through more recent changes in diagnostic criteria and better surveillance."
"Whether NICU graduates represent a different phenotype from other children with ASD requires additional confirmation, but, at the least, these findings support the view that studying this cohort prospectively may yield insights into underlying mechanisms and behavioral precursors to ASD," the authors concluded.