Children who are born more than three months premature have double the expected rate of autism at age two as full-term children, according to a study published Wednesday in the Journal of Pediatrics.
Twenty-six percent of babies born extremely premature had cognitive impairment, according to the study.
Overall, about one in 10 of the extremely premature infants who did not have other health problems (including cerebral palsy, mental impairment, or vision or hearing problems) tested positive for autism at age two.
The study assessed the children via a survey of behavior known as the Modified Checklist for Autism in Toddlers (M-CHAT). But not all children who test positive definitely have the brain development disorder. Autism spectrum disorders (which include a range of diagnoses, from mild to more severe autism) aren't typically diagnosed until age three or older, and M-CHAT is not considered a definitive test.
However, the finding is not surprising, according to Dr. Antonio Hardan, director of the Autism and Developmental Disabilities Clinic at the Lucile Packard Children's Hospital at Stanford University, who was not involved in the study.
"We have to be in the womb for nine months for a good reason," says Dr. Hardan. "There are a lot of steps of brain development that should occur in the right environment, and the ideal environment is in the womb." Health.com: Depression during pregnancy doubles risk of preterm birth
In the new study, which was conducted by a team led by Karl Kuban of the Boston University Medical Center and Boston Medical Center, 26 percent of children who were born extremely premature (27 weeks gestation or less, as opposed to a full-term of 37 weeks or more) had cognitive impairment, 11 percent had cerebral palsy, 3 percent had problems with vision, and 2 percent had hearing impairment.
Overall, 21 percent tested positive for possible autism when given the M-CHAT at age two. However, when the researchers excluded all children with cerebral palsy or other health problems, 10 percent of the extremely premature children tested positive for autism. About 5.7 percent of children who aren't premature test positive on M-CHAT.
Hardan said in addition to brain development, premature birth also cuts short crucial nutritional and hormonal support.
"You put together being born at 27 weeks, prenatal complications, and the possibility of genetic vulnerabilities, and all these factors will add up to launch the process that can lead to autism," he said. Health.com: Do vaccines really cause autism?
Over the past decade, some research has suggested that autism may be on the rise. Hardan said that more awareness of autism, as well as a broadening of the definition of the condition, have played a role. However, the fact that more premature infants are surviving than in the past may have also contributed to autism rates, he said.
"Twenty or 30 years ago, the survival rate of a baby born premature was much less than it is now," he said. "Today, thanks to medical advances, we are seeing these premature babies at age nine, or as teenagers, with emotional and behavioral symptoms similar to autism."
Lori Warner, director of Michigan's Beaumont Hospital's HOPE Center, works with premature children who show signs of an autism spectrum disorder. The symptoms include a lack of eye contact, pointing and social interest. However, sluggish motor skills in an infant or toddler do not automatically mean a child has autism.
"Motor milestones [such as lack of eye contact] are often delayed in premature kids," she said. "But we expect that a premature baby will not have any more complications by age two."
If a child still has signs of autism past the second birthday, such as withdrawing from peer relationships, lack of speech, using repetitive language, and a persistent fixation on certain objects, it could mean he or she has autism. Health.com: How My Son's Autism Changed Everything
"Kids without autism still have social interest, even if they have difficulty, but with autism, social communication skills are impaired or absent," Warner said.
Although there is no cure for autism, treatment is available, and the earlier the better. Hardan and Warner recommend a formal evaluation for children if caregivers suspect something is wrong.
"You can go through the school system-- it's free," Warner said. "It's important to get a good handle on what the impairments are."
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