Research from the US suggests that compared to other developmental disabilities, low birthweight and premature birth was linked to a higher risk of autism, especially for girls.
The study was the work of Drs Diana Schendel and Tanya Karapurkar Bhasin, of the National Center on Birth Defects and Developmental Disabilities, at the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, and is published in the June 2008 early online issue of the journal Pediatrics.
The study had two goals. The first was to find out how frequently autism prevailed compared to that of other developmental disabilities in low birthweight and preterm babies, and the second was to establish the specific risks involved.
For the first goal, Schendel and Bhasin counted all children born in Atlanta between 1981 and 1993 who survived until the age of three. These were located from vital records.
From this group they then identified those that were still living in Atlanta at age between 3 and 10, and who had developmental disabilities: autism, mental retardation, cerebral palsy, hearing loss, or vision impairment. They used another set of records for this, the Metropolitan Atlanta Developmental Disabilities Surveillance Program.
For the second goal, the researchers looked at records from the first goal and created a “nested case-control sample”, with those children identified as having autism being the “cases”, and those who were not identified as having a developmental disability (or in receipt of special education) as the “controls”. (It is a nested sample because these groups are subgroups of the overall cohort). Over 550 case-control pairs were created.
The results showed that:
- Compared to other developmental disabilities, the prevalence of autism in preterm or low birthweight children was significantly lower.
- Birthweight below 2.5 kg (5.5 lbs) and birth at less than 33 weeks gestation was linked to a twofold increase in autism risk.
- This increased risk of autism was higher in girls and when autism was accompanied by other developmental disabilities.
- For example, there was a significant fourfold risk of autism in low birthweight girls who also had mental retardation, whereas there was no significant increased risk in low birthweight boys for autism alone.
The authors concluded that:
“Gender and autism subgroup differences in birth weight and gestational age, resulting in lower gender ratios with declining birth weight or gestational age across all autism subgroups, might be markers for etiologic heterogeneity in autism.”
Schendel told Bloomberg in a telephone interview last week that their findings suggest:
“There may be sex differences in genetic factors leading to autism.”
“Girls may need an additional ‘insult’ before birth that could include reduced growth or premature birth,” said Schendel.
Low birthweight and pre-term birth are already known to be among the biggest risk factors for developmental disabilities, said Schendel, who recommended that children in this group should also be monitored carefully for behavioural problems because of the higher prevalence of autism.
“Birth Weight and Gestational Age Characteristics of Children With Autism, Including a Comparison With Other Developmental Disabilities.”
Diana Schendel, and Tanya Karapurkar Bhasin.
Pediatrics, Vol 121, No 6, pp 1155-1164, June 2008
DOI:10.1542/peds.2007-1049
Source: journal abstract, Bloomberg.
Written by: Catharine Paddock, PhD