Caesarean, Autism and ADHD

A review of more than 60 studies and 20 million births has found that caesarean birth is linked to a higher risk of autism spectrum disorder and attention-deficit hyperactivity disorder in kids. The international review, which includes Australian studies, shows kids have 33 per cent higher odds of developing autism spectrum disorder and 17 per cent higher odds of developing ADHD if they are born by c-section. Whether the c-section delivery was elective or emergency made almost no difference to the odds of developing these disorders. The researchers say understanding why this link might occur will be important given the increase in C-section rates.
​Research link  HERE: 

Reaction and consideration.
The findings of this large study are significant, interesting and require consideration. However as with all research it requires scrutiny and with much research further study and investigation to clarify the findings implications.

Some considerations.
Autism has had an association with Pre-term birth, and LSCS (Lower Segment Caesarean Section) is associated more commonly with pre-term birth to avoid physical complication or stresses upon the baby.
This is one factor that can compounded by uncorrected over view studies.
The 63 papers that contribute the body of evidence of which this association has been drawn has little reference to whether adjusted corrections have been made or considered in reference to the conclusion results. That is not to underplay the findings, they are significant and of interest but dictate clarification and further assessment.

Assoc. Prof. Jason Howitt of Swinburne University identifies concerns that some of the studies had high rates of autism not consistent with the general population and suggests heavy bias as it is " not consistent with worldwide rates of autism of between 1-3% of all birth." In some studies included in this research the rates were between 10-70%.

Professor Jeffrey Keelan acknowledges the significance of the study but that the researchers have been unable to adequately adjust for many factors that may link outcome with birthing method. He reiterates that further evaluation and research is need to clarify the findings.

Dr Alex Polyakov is a Senior Lecturer in the Department of Obstetrics and Gynaecology at The University of Melbourne and a Consultant Obstetrician, Gynaecologist and Fertility Specialist
"It is a meta-analysis which combined data from 61 studies that included more than 20 million deliveries. The authors reported a statistically significant association between caesarean delivery and autism spectrum disorders as well as ADHD. Other psychiatric disorders did not demonstrate a statistically significant association with the mode of delivery. The methods employed in meta-analysis have been criticised recently. This criticism is usually centred on the fact that a number of unrelated studies, which employed a variety of methodologies, populations and statistical analysis techniques are combined to produce a point estimate of risk. The legitimacy of such data manipulation must be questioned and its results are usually of doubtful exactitude. This can easily be demonstrated if one was to examine two largest individual studies included in the autism spectrum disorders (ADH) and ADHC meta-analysis.
 
ADH
A study by Curran et al was conducted in Sweden between 1982 and 2011 and used ICD-9 and ICD-10 to define ADH and examined 2,697314 deliveries, 28,290 children were diagnosed with ADH. This translates to a prevalence of ADH of 1.05% in this population. This is the largest study in this meta-analysis. The second-largest study was by Yip et al and was conducted in Norway and Finland between 1984 and 2004. It used ICD-8, 9 and 10 to define ADH and included 1,052,397 deliveries with 1,303 children being diagnosed with ADH. In this study, which is the second-largest included in this meta-analysis, the prevalence of ADH was 0.12%, approximately 10 times less than reported by Curran et al. This demonstrates the pitfalls of combining radically different studies to try to arrive at a meaningful conclusion.
 
ADHD
The above exercise can be repeated with the ADHD portion of the article. If the two largest studies included are examined, the prevalence of ADHD in one was 2.77%, while in the second-largest sample it was 0.2%, again a tenfold difference.
 
What can be concluded from these discrepancies in the prevalence of the two diagnoses? Firstly, even if the final results are accepted, it is almost impossible to assess their clinical significance. A 20% increase in risk has radically different meanings, depending on the prevalence of a particular outcome. For example, a 20% jump from a baseline of 3%, will translate into 3.6%, probably a clinically significant increase, that would warrant an intervention to prevent it. On the other hand, the same 20% increase, if applied to the baseline rate of 0.2%, will result in 0.24% prevalence, which may not be as clinically troublesome and may not warrant an intervention.
 
Secondly, one must question the wisdom of combining such divergent studies and expecting an accurate and unbiased estimation of risk. The old saying from computer science: 'garbage in, garbage out' seems to apply, as poor quality input will invariably produce sub-optimal output.
 
Overall, it must be stated that both caesarean section and vaginal delivery have risks for mothers and babies. These risks are not the same and there is no consensus as to which mode of delivery is better overall. The study adds another possible risk to indiscriminate utilisation of caesarean section as the preferred mode of delivery, but it must be balanced against recognised risks of alternative delivery strategies."

Emeritus Professor Alastair MacLennan AO (head of Australian Collaborative Cerebral Palsy Research group and University of Adelaide) also identifies a cautionary overview.
"Although an interesting and controversial topic the many methodological weaknesses of this study make any conclusion very unreliable.

Firstly no realistic physiological mechanism for the weak association of autism and ADHD with mode of delivery is offered.

The studies analysed were very different (heterogeneous) and all were observational studies that do not allow for a wide variety of potential biases.

As a general rule for outcomes in observational studies to be plausibly significant the Odds Ratio (times difference) should be more than 2 and the confidence intervals should not cross one. In this study, the ASD odds ratio was only 1.33 and ADHD was only 1.17.
For all the other outcomes examined the confidence intervals crossed one meaning that there was no statistical significance."

In summary, it is a large study with an interesting and well-performed metaanalysis of neurodevelopment outcomes on an impressively large number of deliveries (over 20 million) from over 60 studies performed across 19 different countries. The central findings are that caesarean section deliveries are associated with a 33% increase in risk of autism spectrum disorder (ASD) and a 17% increase in attention-deficit/hyperactivity disorder (ADHD).
​The issue is: can a casual connection and link be drawn based on the evidence? Further research is required.