A new study based on combining data from 20 million births has found that cesarean delivery is linked to autism spectrum disorder (autism) and attention deficit hyperactivity disorder (ADHD).
However, the study does not indicate that cesarean delivery causes autism or ADHD . The truth is much more difficult to decipher and it serves to illustrate that correlation does not imply causality.
What are these disorders?
Autism and ADHD are what we know as neurodevelopmental disorders that involve clear differences in the behavioral development of people, which is supposedly due to differences in the brain.
In the case of autism, behavioral differences occur in the part of the brain that is primarily responsible for social and communication development. In the case of ADHD, these differences affect the ability to control and direct attention.
The exact reasons why the brain develops differently are not entirely clear. Through studies in twin brothers we can understand the role of genetics and environmental influences on specific traits and thanks to this type of studies we know that both autism and attention deficit hyperactivity disorder have a significant genetic load.
However, these studies have also pointed out that there are environmental influences , such as bacterial or viral infections during pregnancy, which are likely due to interactions with genetic makeup.
What are the results of this research?
The relationship between some cesarean deliveries and autism has been known for nearly two decades, although any relationship to ADHD has been less investigated and more studies are needed in this field.
The study we are reviewing today, published in the scientific journal JAMA Network Open, combines all the studies conducted to date into a single analysis. This meta-analysis has allowed researchers to determine the extent to which there is a relationship between cesarean deliveries, autism, and attention deficit hyperactivity disorder .
In this case, the meta-analysis included more than 20 million individuals and concluded that babies born by caesarean section were more likely to be diagnosed with autism or ADHD during early childhood.
While these associations are scientifically sound, they carry little weight. Children born by cesarean section were 1.33 times more likely to be diagnosed with autism and 1.17 times more likely to be diagnosed with ADHD.
If we take into account that the prevalence of these diseases is already quite low (close to 1% in the case of autism and 7% for ADHD), this increase in the probabilities is not substantial. In the case of autism, this increase in the possibilities is not relevant and does not call for a change in current clinical practices.
This association was similar in the case of children born by both elective and emergency cesarean section.
What does this all mean?
The problem with these types of findings is that it is very tempting to draw conclusions between one factor (cesarean birth) and another (autism or ADHD) . Unlike other areas of knowledge, the conclusions are easy to understand and the implications appear to be obvious.
But this simplicity is misleading and tells us more about our desire for simple answers than it does about the truth of science.
The studies included in this meta-analysis used a branch of science known as epidemiology that studies how often diseases and disorders occur in different groups of people, their causes, and how to prevent or manage them.
Epidemiological studies analyze large numbers of the population to determine trends in the results that indicate the possibility that a certain factor coincides with a specific disorder to a greater extent than it would respond randomly.
In this case there is the observation that people with autism or ADHD are more likely to have been born by cesarean section than we would normally expect.
But this type of epidemiological study is unable to determine whether one factor (cesarean section) causes another (ADHD or autism).
There are two main reasons:
First, we cannot rule out the existence of a third factor influencing this association. For example, we know that cesarean deliveries are more common in older and obese pregnant women, as well as those with a history of immune diseases such as asthma.
All of these factors have also been linked to an increased chance of having a child with autism, and it is entirely possible (some would say likely) that these factors actually indicate a relationship between cesarean delivery and neurodevelopmental disorders.
The second reason is that this type of epidemiological study is unable to provide what scientists call a “mechanism”: that is, a biological explanation to determine why such an association exists.
A study of mechanism in this field could be the exploration of biological differences in newborns, either born naturally or by cesarean section, and understand the way in which these differences may signify atypical behavioral development.
In the absence of a solid body of evidence from these types of studies, there is simply no scientific basis to conclude that there is a causal link between cesarean delivery and neurodevelopmental disorders .
What conclusions should we draw from this study?
This study provides us with a good basis to conclude that there is a statistical link between cesarean delivery on the one hand and autism and attention deficit hyperactivity disorder on the other. But that’s it.
We still don’t know why this link exists , but cesarean delivery alone almost certainly does not contribute to a child’s chances of developing autism or ADHD.
Instead, other pregnancy factors are likely to play a role in this cause-effect relationship, as well as genetic factors that may interact with environmental influences during pregnancy that contribute to brain development.
Author: Andrew Whitehouse, Bennett Chair in Autism, Telethon Kids Institute, University of Western Australia
This article was originally published on The Conversation. You can read the original article here
Translated by Silvestre Urbón
Fotos | iStochphoto
