passionless Droning about autism

Posts Tagged ‘Intriguing

Hello friends –

I ran across this one on accident the other day (why wasn’t it in one of my pubmed alerts?):

Gestational Age at Delivery and Special Educational Need: Retrospective Cohort Study of 407,503 Schoolchildren

Background

Previous studies have demonstrated an association between preterm delivery and increased risk of special educational need (SEN). The aim of our study was to examine the risk of SEN across the full range of gestation.

Methods and Findings

We conducted a population-based, retrospective study by linking school census data on the 407,503 eligible school-aged children resident in 19 Scottish Local Authority areas (total population 3.8 million) to their routine birth data. SEN was recorded in 17,784 (4.9%) children; 1,565 (8.4%) of those born preterm and 16,219 (4.7%) of those born at term. The risk of SEN increased across the whole range of gestation from 40 to 24 wk: 37–39 wk adjusted odds ratio (OR) 1.16, 95% confidence interval (CI) 1.12–1.20; 33–36 wk adjusted OR 1.53, 95% CI 1.43–1.63; 28–32 wk adjusted OR 2.66, 95% CI 2.38–2.97; 24–27 wk adjusted OR 6.92, 95% CI 5.58–8.58. There was no interaction between elective versus spontaneous delivery. Overall, gestation at delivery accounted for 10% of the adjusted population attributable fraction of SEN. Because of their high frequency, early term deliveries (37–39 wk) accounted for 5.5% of cases of SEN compared with preterm deliveries (<37 wk), which accounted for only 3.6% of cases.

Conclusions

Gestation at delivery had a strong, dose-dependent relationship with SEN that was apparent across the whole range of gestation. Because early term delivery is more common than preterm delivery, the former accounts for a higher percentage of SEN cases. Our findings have important implications for clinical practice in relation to the timing of elective delivery

[Full paper from link.  Emphasis is mine]

Essentially the authors evaluated gestational lengths with a fine tooth comb to discern if ‘early’, though not technically ‘pre-term’ delivery was associated with a ‘special education need’ (SEN), which in this case embodies a range of developmental problems including dyslexia, autism, or even physical problems like deafness or vision problems.

What the authors found was that there were subtle, but real effects in the likelyhood of having a special education need for non full term births that was dose dependent, but even included children that would not necessarily be considered early by existing standards.

Our study demonstrated a strong trend of decreasing risk of SEN with advancing gestational age at birth. The key finding of the present analysis is that this trend continued across gestational ages classified as term. Although the risk of SEN was highest among infants who were delivered preterm (<37 wk gestation), these accounted for only 5.1% of deliveries. Therefore, only a relatively small proportion of SEN (3.5%) could be attributed to preterm delivery. By contrast, 39.6% of infants were delivered between 37 and 39 wk gestation. Therefore, whilst these early term infants had only a moderately increased risk, 5.3% of SEN cases could be attributed to early term delivery.

The authors claim that the finding of effects at early, but not pre-term gestational  lengths is one that is largely  missing from existing studies, which have not taken these date ranges into consideration, or the ones  that did, were not studying for cognitive problems, and indeed, excluded children with these criteria.  Curiously, they also report an increase in SEN in children who had extra gestational periods, i.e., > 41 weeks in some studies.

The authors make absolutely no speculation as to what might be driving increased special education needs as the result of premature or early birth.

Looking at their results, one of the most striking things is that the impact did not alter if elective (i.e. C-Section) versus non-elective births were used as a variable. But this has deep ramifications for the autism storyline, which holds that if there are environmental factors that can contribute to autism, they are prenatal, and indeed, are often thought to involve insults very early in the prenatal period.  In this case, we know that a genetic or environmental force isn’t contributing to the early birth, because it didn’t matter if the birth was spontaneous or not.  The only area for an effect is postnatal. That is a big, big difference in the narrative.

Is this a matter of some just in time epigenetic programming happening in the womb that doesn’t get a chance to finish up in early births?  Alternatively it could be that early birth allows for environmental exposures that the infant is not quite prepared to deal with.  Or it could be both, or neither, or an illusory finding, but if these findings can be replicated, it raises a lot of questions about the sacred line between prenatal and postnatal environmental influences.

Unfortunately, the raw data for this project  doesn’t seem to be available online; it might be really nice to see if there were patterns to be observed had particular salience to our population of interest.

–          pD

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