Size and Growth of Babies Offer New Clues Into Autism

Low birthweight and rapid infant growth are both linked to autism spectrum disorders

/ Author:  / Reviewed by: Joseph V. Madia, MD

The signs of autism are met with distress and concern for most parents. Avoiding eye contact, not responding to their names, lack of interest in objects and delayed speech skills are all symptoms of autism, that show up before age three.

Some children who end up diagnosed with autism spectrum disorders (ASD) may show hints of problems within the first few months of life, but most seem to develop normally until around 18 to 24 months, when symptoms begin showing up. While there is currently no cure for ASDs, doctors and researchers are beginning to find new clues and links into the development of the disorder.

Low Birth Weight and Autism

Low birthweight may have a lot to do with autism. Researchers at the University of Pennsylvania School of Nursing have found that premature, low birthweight infants are five times more likely to have autism than babies born at normal weights.

The study is one of the most remarkable of its kind, because it followed individuals for 21 years. The 862 children who were part of the study were born in three New Jersey counties between 1984 and 1987; each had birthrights from 500 to 2,000 grams, or about one pound to a maximum of 4.4 pounds. The babies were followed into early adulthood and over that time, researchers found that five percent of the children were diagnosed with autism - compared to one percent of the general population.

“Emerging studies suggest that low birthweight may be a risk factor for autism spectrum disorders,” said lead author Jennifer Pinto-Martin, MPH, PhD, director of the Center Centers for Autism and Developmental Disabilities Research and Epidemiology at Penn Nursing.

“Cognitive problems in these children may mask underlying autism,” Dr. Pinto-Martin added. Previous research has shown a link between low birthweight and many cognitive development problems. “If there is suspicion of autism or a positive screening test for ASD, parents should seek an evaluation for an ASD. Early intervention improves long-term outcome and can help these children both at school and at home.”

Faster Growth and Autism

At the other end of the spectrum, a phenomenon that is also shedding light on the mysteries of autism is rapid growth. A recent study at the Yale University Child Study Center has found that boys with autism tend to grow faster as babies. The Yale research found that male infants with autism had larger head size and weight than normally developing babies, as prior research has also shown; but this new study found accelerated growth throughout the rest of the body as well, for autistic boys.

The Yale research team, led by Katarzyna Chawarska, analyzed the medical records of 64 children with autism, along with 65 boys with other development problems and 55 typically developing kids. Boys with autism were longer at five months of age, had a larger head circumference at 9.5 months and weighed more by their first birthday. None of the children with developmental problems other than autism showed similar growth patterns.

Boys with brain and body "overgrowth" tend to have more severe autism symptoms, particularly involving social skills, than autistic children who don't grow faster than normal.

Chawarska says the findings offer new clues to the underlying mechanisms of autism, and that it's possible this overgrowth is one of the causes of autism. It could contribute to worsening ASD symptoms or even represent a subtype of autism that's marked by both accelerated growth and severe social deficits.

"We need to ask why growth factors may be dysregulated in autism," Chawarska said. "And that's something we have no answer to now." She adds that although pediatricians should pay close attention to infants with accelerated growth, it should not be used to make a diagnosis of autism. She plans to conduct a similar study on girls.

Review Date: 
October 14, 2011