(CBS) Parents who wonder if their baby is autistic sometimes look for red flags like poor eye contact and a lack of smiling - things that can be hard to determine in infants.
But a new study suggests that a more reliable way to tell which babies are at risk for autism might be to look for a pair unusual characteristics, according to HealthDay.
The study found that infants who were later diagnosed with autism often exhibited abnormal muscle tone - limbs that are too rigid or too floppy - and abnormalities in visual processing.
The differences were so subtle parents might not easily spot them, co-author of the study, Ira Cohen, chair of the psychology department at the New York State Institute for Basic Research in Developmental Disabilities, told HealthDay.
The study, published in the September issue of "Pediatrics," followed 28 babies who spent time in the neonatal intensive care unit (NICU) and were later diagnosed with an autism spectrum disorder.
At one month, 40% of the infants later diagnosed with autism showed abnormalities in the way they visually tracked objects, and more than 50% had abnormal muscle tone in their arms.
It's worth mentioning that many infants who exhibited these characteristics turned out to develop normally. However, the percentage of those who were autistic was significant.
More studies are needed, researchers say, on healthy babies that were not in the NICU to begin with.
Autism is characterized by problems with social interaction, communication and restricted interests, according to the National Institute of Neurological Disorders and Stroke. Recent estimates put the number of U.S. children with the disorder at one in 110, a number that has climbed steadily since the 1980s.