Premature babies and autism risk

Children born extremely preterm may face a much higher-than-average risk of developing autism later in childhood.

Past research has shown that children born prematurely have a higher prevalence of autism spectrum disorders (ASDs), but the extent of the risk linked to extreme prematurity has not been clear. This study shows not only a substantially heightened risk among children born very preterm, but also points to which of these children are most likely to be affected.

ASD refers to a group of developmental disorders that hinder people's ability to communicate and build relationships. The conditions range from severe cases of classic autism to Asperger's syndrome - a disorder in which a person has normal intelligence and verbal skills, but difficulty socialising and understanding subtler forms of communication, like body language and vocal tone.

Researchers from UK studied 219 children born before the 26th week of pregnancy and found that 8 percent met the criteria for an ASD at age 11. That compared with none of 153 classmates who were born full-term and included in a comparison group. The ASD rate was far higher than that in the general population, which experts estimate to be somewhere between one and nine cases per 1,000 children, depending on how strictly the disorders are defined.

The findings show an increased frequency of ASD, but it is mainly among children with other disabilities, such that the risk of it developing in children with no other problems is very low. For example, 56 of the children in the extremely preterm group had no impairments in thinking and learning when the researchers assessed them at the age of 6. None of those children met the criteria for an ASD diagnosis at age 11.

In contrast, of the 34 children with moderate to severe cognitive impairment at age 6, 18 percent were diagnosed with an ASD at age 11. Of the 65 children with mild impairment, 6 percent were later diagnosed with an ASD. Most of the children with ASD were diagnosed with classic autism, while three were diagnosed with what is known as pervasive developmental disorder "not otherwise specified" - where children have some, though not all, of the characteristics of autism. None of the children had the milder Asperger's disorder.

Medical advances have meant that more and more very premature and low-birth weight newborns are surviving. Still, they face increased risks of delayed development, learning disabilities and behavioral problems later on.

We know that very-preterm babies' brains develop differently to those of full-term babies after birth, and that this is associated with a high frequency of cognitive problems in childhood. The impaired brain development in these children may account for the high ASD risk. And that means that autism may arise via different mechanisms in extremely preterm children compared with those who were born full-term - for whom genetics are believed to be key. For parents of children born extremely preterm, the findings mean that they should be aware of the possibility that their child's learning or behavioural issues could be indicative of an ASD.

Where a parent is worried about learning or behavioural problems in their very premature baby, they should seek advice from a professional to see what the nature of these problems is.