A quote to begin: "There was no association between planned CS [Caesarean section] and ASD [autism spectrum disorder]... or ADHD [attention-deficit hyperactivity disorder]." And further: "There was no association between mode of delivery and ASD or ADHD in this cohort."
Those were the conclusions reached in the paper by Eileen Curran and colleagues  who sought to look at whether the route of entry into the world may influence offspring risk of autism or ADHD. Based on data derived from The Millennium Cohort Study (MCS), a longitudinal survey covering the birth period and "including 13,141 children", researchers dived into the treasure trove of collected information to see whether "birth by Cesarean section (CS) and induction of labor (IOL)" correlated with later childhood outcomes. Probably not was the answer coming back, or at least not in any generalisable sense. Indeed, other recent research has also suggested similar things .
This is interesting research. Not least because I've discussed other work from this research group on this topic before on this blog (see here) based on their systematic review and meta-analysis of the available data up to February 2014 . Up until then, the message was a cautious: "Delivery by CS is associated with a modest increased odds of ASD, and possibly ADHD, when compared to vaginal delivery."
At this point I'd also like to introduce another recent paper from this authorship group  further adding to this debate about birth method and offspring risk (or not) of autism. Based on data derived from the "Swedish Medical Birth Register and the Swedish National Patient Register" providing information on perinatal factors and ASD diagnosis respectively, the authors concluded that whilst "children born by CS are approximately 20% more likely to be diagnosed as having ASD", this association dwindled somewhat when "using sibling controls." Ergo, the correlation between birth by C-section and autism diagnosis is likely "confounding by genetic and/or environmental factors." A good write-up of the study can be seen here.
So, based on two pretty large (participants in the thousands) studies, geographically separate (UK vs. Sweden), the suggestion that birthing method might affect autism risk turns out to be not as strong as originally suggested and with it a reminder that meta-analyses are only as strong as the data they include. I know most people with their eyes and ears to the autism research scene probably won't be shocked by these results and the almost pantomime-like state ('oh yes it is, oh no it's not') of various aspects of autism research. As has been noted on some occasions, autism research seems to have a reproducibility crisis of its own to contend with.
But in all of that a few reminders: autism is a very heterogeneous condition (remember the autisms) and just because there is not population-wide effect does not mean that variable A, B or C is all bunk when it comes to 'some' autism (see here). Oh, and baby and bathwater - as in, don't throw them both out - should also be remembered ...
And now... Star Wars.
 Curran EA. et al. Obstetrical Mode of Delivery and Childhood Behavior and Psychological Development in a British Cohort. J Autism Dev Disord. 2015 Sep 28.
 Robson SJ. et al. Childhood Health and Developmental Outcomes After Cesarean Birth in an Australian Cohort. Pediatrics. 2015. October 12.
 Curran EA. et al. Research review: Birth by caesarean section and development of autism spectrum disorder and attention-deficit/hyperactivity disorder: a systematic review and meta-analysis. J Child Psychol Psychiatry. 2015 May;56(5):500-8.
 Curran EA. et al. Association Between Obstetric Mode of Delivery and Autism Spectrum Disorder: A Population-Based Sibling Design Study. JAMA Psychiatry. 2015 Sep 1;72(9):935-42.
 Chien LN. et al. Risk of autism associated with general anesthesia during cesarean delivery: a population-based birth-cohort analysis. J Autism Dev Disord. 2015 Apr;45(4):932-42.
Curran, E., Cryan, J., Kenny, L., Dinan, T., Kearney, P., & Khashan, A. (2015). Obstetrical Mode of Delivery and Childhood Behavior and Psychological Development in a British Cohort Journal of Autism and Developmental Disorders DOI: 10.1007/s10803-015-2616-1