Wednesday, 10 December 2014

Maternal smoking during pregnancy and offspring autism: no measurable association but...

Oh. Yes sir. How doth the little
bumblebee improve each...
"We found no evidence to support a measurable association between maternal prenatal smoking and ASD [autism spectrum disorder] in offspring."

That was the conclusion reached in the meta-analysis published by Brittany Rosen and colleagues [1] looking at the collected peer-review literature examining any correlation between maternal tobacco smoking during pregnancy and risk of offspring receipt of a diagnosis of autism or ASD. Based on a review of 15 studies in this area, researchers concluded that there was very little to see when it came to any association: "summary OR [odds ratio] 1.02, 95 % CI [confidence intervals0.93–1.12".

I think most people nowadays have probably seen or heard of the messages about the potential dangers of smoking during pregnancy and the benefits of abstaining/quitting to both mother and unborn child. That's not to say however that every mum-to-be has understood the risks as per the findings from Cnattingius [2]. Indeed without being judgemental, even at rare visits to my own local hospital, I have seen heavily pregnant women puffing away outside the maternity unit and can't help wondering why, particularly when so many alternatives or quitting aids (with caveats) are available these days.

Insofar as the various investigations into smoking with offspring autism in mind, there is quite a bank of research in this area. That's not to say that the evidence is all one-way when it comes to smoking during pregnancy and offspring risk of autism as per studies like the one from Phuong Lien Tran and colleagues [3] (open-access) who concluded that smoking during the whole of pregnancy might have a modest impact on autism risk, at least in Finland. The findings reported by Visser and colleagues [4] on smoking during pregnancy appearing to "contribute more to broadly defined (PDD-NOS) than to narrowly defined ASD (AD)" are also worthwhile including in these days of phenotypes and plural autisms. Indeed, the report from Amy Kalkbrenner and colleagues [5] (open-access) continues the theme: "The possibility of an association with a higher-functioning ASD subgroup was suggested, and warrants further study."

On the basis of these studies and others [6], I'd be minded to suggest that whilst the Rosen findings are reassuring for the more general concept of risk (i.e. autism overall) the message about quitting smoking before and during pregnancy as potentially affecting offspring autism risk, is not yet settled when it comes to specific types of autism or specific places on the autism spectrum being implicated. I say this not to add to any further burden about this or that 'causing autism' as per examinations on things like maternal infection during pregnancy (see here) or C-sections (see here) or maternal diabetes (see here) for example, but rather using science as a potential informer in raising awareness of this possible outcome. Indeed, if one is to assume that the [preliminary] evidence on air pollution and genetics mixing might also impact on autism risk (see here), the question of whether direct inhalation of several thousand pollutants can impact on foetal outcomes becomes rather more compelling including whether risk of certain comorbidity appearing alongside autism might also be influenced [7].

Oh, and father's tobacco habits might also be important [8]...

Music, and something quiet from Henry Rollins (not)...

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[1] Rosen BN. et al. Maternal Smoking and Autism Spectrum Disorder: A Meta-analysis. Journal of Autism and Developmental Disorders. 2014. November 29.

[2] Cnattingius S. The epidemiology of smoking during pregnancy: smoking prevalence, maternal characteristics, and pregnancy outcomes. Nicotine Tob Res. 2004 Apr;6 Suppl 2:S125-40.

[3] Tran PL. et al. Smoking during pregnancy and risk of autism spectrum disorder in a Finnish National Birth Cohort. Paediatr Perinat Epidemiol. 2013 May;27(3):266-74.

[4] Visser JC. et al. Narrowly versus broadly defined autism spectrum disorders: differences in pre- and perinatal risk factors. J Autism Dev Disord. 2013 Jul;43(7):1505-16.

[5] Kalkbrenner AE. et al. Maternal smoking during pregnancy and the prevalence of autism spectrum disorders, using data from the autism and developmental disabilities monitoring network. Environ Health Perspect. 2012 Jul;120(7):1042-8.

[6] Habek D. & Kovačević M. Adverse pregnancy outcomes and long-term morbidity after early fetal hypokinesia in maternal smoking pregnancies. Arch Gynecol Obstet. 2011 Mar;283(3):491-5.

[7] Kovess V. et al. Maternal smoking and offspring inattention and hyperactivity: results from a cross-national European survey. Eur Child Adolesc Psychiatry. 2014 Nov 21.

[8] Laubenthal J. et al. Cigarette smoke-induced transgenerational alterations in genome stability in cord blood of human F1 offspring. FASEB J. 2012 Oct;26(10):3946-56.

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ResearchBlogging.org Rosen BN, Lee BK, Lee NL, Yang Y, & Burstyn I (2014). Maternal Smoking and Autism Spectrum Disorder: A Meta-analysis. Journal of autism and developmental disorders PMID: 25432101