Monday, 19 March 2012

Gestational age at delivery and special educational need

An article by Boyle and colleagues* (full-text) published in the BMJ provided some food for thought recently with the conclusion that even babies born at what would be considered term (37-38 weeks) may suffer from poorer health than those born at 39 - 41 weeks. To me this seems like a very narrow window when it comes to something like birth timing and future health outcomes bearing in mind what risk means and the myriad of potential confounding variables.

Autism is not specifically mentioned in the Boyle article but nevertheless there is some opinion on a possible relationship between gestational time and associated risk. Indeed, I don't know about you but to me it seems like almost every week a new study is published suggesting that adverse conditions at birth might place a person at elevated risk of developing an autism spectrum condition. OK perhaps I over-exaggerate with the 'every week' bit but certainly this is a recurring theme. As if to prove a point take a look at this paper recently published by Movsas and Paneth** on gestational age and symptom severity in autism.

There are other examples suggesting that low birth weight increases the risk, breech presentation, planned caesarean section, hyperbilirubinema... the list goes on. Indeed so numerous are the factors, studies and accompanying media reports that I very often don't even read them in their entirety anymore given the wealth of evidence that is being built up around our entrance into the world.

On the one hand, in a world full of questions about autism - its aetiologies (plural) and natures - such reports have contributed to a valuable area of research with regards to risk and also potentially mechanisms pertinent/contributory to at least some cases. With a condition which has by far raised more questions than science has currently answered, these kinds of 'pointers' might turn out to be important ones.

On the other hand, there does seem to be a tendency to present this relationship slightly out of context; in that autism receives all the attention in relation to something like premature/pre-term babies yet at the expense of a much larger relationship between something like birth dates and special educational needs (SEN) as a whole.

To illustrate this point, my attention turned to quite a powerful study published a few years back by MacKay and colleagues** (full-text) which looked at the rate of SEN based on population registry data where detailed birth data was also present. I should at this point describe a few details about how things worked.

The study was conducted in Scotland which, at the moment, is still part of the United Kingdom (UK). For those unfamiliar with UK healthcare system, we have the National Health Service (NHS) which is paid for through direct taxation and currently means that all citizens, irrespective of income or status, have a right to free healthcare at the point of need. From cradle to grave, each person has a unique NHS number, which alongside some quite copious amounts of note-taking, provides an impressive bank of health information about a person. Health services often overlap with other areas such as social and educational services (most of the time) which can form quite a detailed picture of a citizen as evidence by the Child Health Profiles reports for example which are accessible to all and provide a wealth of information. Having experienced first-hand how much information is gathered at birth and the early years, I can vouch for this being a pretty good system.

In addition, I quote from the study: "Under the Special Educational Needs and Disability Act of 2001, both schools and local education authorities in the United Kingdom have a statutory duty to identify, assess, and make provision for children with SEN". SEN covers quite a lot of diagnostic ground including learning disability, autism spectrum conditions, ADHD, dyslexia and dyspraxia.

So with these details in mind, the study:

  • Based on a large school-aged population covering 19 Scottish local authority areas, details of 514,188 children above 4 years and below 19 years of age were included for study.
  • School census data showing SEN status was linked to the Scottish Morbidity Record (SM2) via birth certificate data.
  • Complete data was available for 362,688 children of whom 17,784 (4.9%) had a record of SEN.
  • In amongst the large amount of results obtained, a few key points were noted including: low birth weight (<2500 g) was associated with an increased risk of subsequent SEN (unadjusted odds ratio [OR] 2.22). This finding was linked to the primary finding that preterm delivery also correlated with risk of SEN, with extreme prematurity (24-27 weeks) carrying the greatest risk (OR = 6.92) steadily declining as children were born closer to their due date but then increasing for infants born overtime after their due date (42 weeks).
  • Importantly, whilst preterm births (<37 weeks) increased the risk of SEN, only a relatively small proportion of SEN was linked to prematurity (5.3%) compared with SEN with a history of 39 weeks gestation (1.7%). 
  • As per the description of SEN, autism as a diagnosis is included. Having said that, no specific data is provided on the distribution of particular diagnoses in the presented dataset so we can't readily ascertain any specific relationship between autism diagnoses and preterm birth from the current paper.

If you have a bit of time free and are interested in this kind of study, I would encourage you to have a look through the MacKay article in its entirety. For me, the important point to take from this study is that autism, some cases of autism, may very well be linked to preterm birth and onward to factors such as birth weight but such a relationship does not appear to be exclusive to autism and might not necessarily take into account other SEN diagnoses working as comorbidities. Perhaps a smaller detail is that with the current lack of a national autism register here in the UK, SEN status with a focus on autism might be a rough-and-ready way to provide a figure on autism rates at least in the UK pediatric population?

To finish, my car journeys are currently filled with the sound of the Beautiful South and the line - She's a PhD in “I told you so,” you've a knighthood in “I'm not listening” as featured in the song Don't marry her (the clean version).

* Boyle EM. et al. Effects of gestational age at birth on health outcomes at 3 and 5 years of age: population based cohort study. BMJ. March 2012
DOI: 10.1136/bmj.e896

** Movsas TZ. & Paneth N. The effect of gestational age on symptom severity in children with autism spectrum disorder. JADD. March 2012.

*** MacKay DF. et al. Gestational Age at Delivery and Special Educational Need: Retrospective Cohort Study of 407,503 Schoolchildren. PLoS ONE. 2010; 7: e1000289.
DOI: 10.1371/journal.pmed.1000289