Autism Risk and low birth weight newborns

19 Oct

A recent article in the journal Pediatrics has gathered a lot of news coverage this week. Prevalence of Autism Spectrum Disorder in Adolescents Born Weighing<2000 Grams

Here is the abstract:

Objective: To estimate the diagnostic prevalence of autism spectrum disorders (ASDs) in a low birth weight (LBW) cohort.

Methods: Participants belonged to a regional birth cohort of infants (N = 1105) born weighing <2000 g between October 1, 1984, and July 3, 1989, and followed up by periodic assessments to 21 years of age. At 16 years (n = 623), adolescents were screened for ASD using a wide net (previous professional diagnosis of an ASD or a score above a liberal cutoff on the Social Communication Questionnaire or the Autism Spectrum Symptoms Questionnaire). At 21 years (n = 189), 60% of screen positives and 24% of screen negatives were assessed for diagnoses of ASD by the Autism Diagnostic Observation Schedule or the Autism Diagnostic Interview–Revised.

Results: Samples retained at ages 16 and 21 years were representative of samples assessed at earlier ages except for lower levels of social risk. Of positive screens, 11 of 70 had ASD; of negative screens, 3 of 119 had ASD. The fractions of the 2 screening groups with ASD (14.3% in screen-positives and 2.5% in screen negatives) were weighted by fractions of screen-positives and screen-negatives among the adolescents (18.8% and 81.2%, respectively). This calculation produced an estimated prevalence rate of ASD in the entire cohort of 5% (31 of 623).

Conclusions: The diagnostic prevalence of ASD in this LBW preterm cohort was higher than that reported by the Centers for Disease Control and Prevention for 8-year-olds in the general US population in 2006.

The idea that low birth wieght might increase risk of autism isn’t new, but this is a different design: following a low birthweight cohort into adulthood.

The paper, and definitely the media coverage, has some limitiations. A great discussion of this paper and the media coverage can be found at The Biology Files in an article by Emily Willingham: Autism and low birthweight: study–and quote–limitations It’s written much better than I could do, an whatever I’d write at this point would just be a distillation of it.

This is different from the risk of autism due to premature birth, something the media mixed up on occasion and that Emily Willingham discusses in her article.

There are certainly some concerns about how the 5% figure was derived, and one can’t really make a direct comparison between a closely watched cohort at adulthood to the prevalence of 8 year olds based on record review (as in the CDC prevalence estimates). However, the idea that low birth weight is a risk factor is worth investigation.

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4 Responses to “Autism Risk and low birth weight newborns”

  1. RAJ October 20, 2011 at 09:11 #

    There are no concerns about how the 5% figure was derived. The study was an NIH funded longitudinal study. The individuals were identified at birth and followed up and periodically examined over several decades. This is one of many studies that will be published over the years and it will give a better understanding of all the types of developmental problems that are associated with low weight birth newborns. The formal autism diagnosis was made using gold standard dagnostic tools (ADOS, ADI-R). In person assessments were made at the Childrens Hospital of Philadelphia or an annex in Princeton NJ.

    Of the 635 LBW babies that were followed up 31 were diagnosed with an ASD using gold standard diagnostic tools and an in-house assesment hence the 5% figure.

    As far as the CDC estimates are concerned, they are based on reviewing school and adminstrative records and none of the 8 year old children contained in the CDC reports are ever examined in person by trained clinicians applying gold standard diagnostic tools. The CDC may overestimating their prevelance rates.

    Fombonne (209) who reviewed all published prevelance studies published since 1966 reported that the most recent studies of ASD prevelance rates are much lower than the CDC data, not 1 100 but are .6 – .7 total ASD with the prevelance of narrowly defined autistic disorder being .2%

    http://www.ncbi.nlm.nih.gov/pubmed/19218885

    Whatever prevelance rates you want to use in comparison, At a minimum the risk for ASD associated with low weight babies is 5% (CDC), even higher if you use Fombonnes meta analysis.

  2. RAJ October 20, 2011 at 12:13 #

    Pinto-Marin’s group have been following the developmental outcomes of Low Birth Weight newborns for decades. They have published previous papers derived from the same group. The prevelance of cerebral palsy is 14.6% far beyond general population norms. In another followup paper, excluding disabled cases, they reported on motor and cognitive outcomes in the group. There was an excess of motor problems compared to population norms. IQ was in the normal range but significantly lower than population norms.

    So what can one make of these studies of developmental outcomes associated low birth weight newborns.

    Low birth weight in newborns is associated with a broad spectrum of neurodevelopmental problems including autism.

    http://www.ncbi.nlm.nih.gov/pubmed/17018463

    http://www.ncbi.nlm.nih.gov/pubmed/7838643

  3. Navi October 24, 2011 at 13:53 #

    I remember not too long ago there was also a study suggesting high birth weight and growth rates… (my autie boy has consistently been in the 95% for height and somewhere between the 70th and 95th for weight – why his enzyme deficiency wasn’t immediately recognized – because he was growing just fine…)

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