A new study based on the combination of data from 20 million births has found that cesarean delivery is related to autism spectrum disorder (autism) and attention deficit hyperactivity disorder (ADHD).
But nevertheless, The study does not indicate that cesarean delivery causes autism or ADHD. The truth is much harder to decipher and it serves to illustrate that correlation does not imply causation.
What do these disorders consist of?
Autism and ADHD are what we know as neurodevelopmental disorders that involve clear differences in people's behavioral development, 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 communicative development. In the case of ADHD, these differences affect the ability to control and direct attention.
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In Babies and more In Spain 25% of C-sections are practiced, twice as recommended by the WHOThe 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 in specific traits and thanks to this type of studies we know that both autism and attention deficit hyperactivity disorder have an important genetic load.
However, these studies have also indicated that there are environmental influences, such as bacterial or viral infections during pregnancy, which are probably due to interactions with the genetic configuration.
In Babies and more A new study finds that the way of birth and cognitive development could be relatedWhat are the results of this research?
The relationship between some cesarean deliveries and autism has been known for almost two decades, although any relationship with ADHD has been less investigated and more studies are needed in this field.
The study we analyzed today, published in the scientific journal JAMA Network Open, combines all the studies conducted to date in a single analysis. This meta-analysis has allowed researchers to determine to what extent there is a relationship between cesarean deliveries, autism and attention deficit hyperactivity disorder.
In Babies and more The time between pregnancies could influence the probability of suffering from autism In this case, the meta-analysis included more than 20 million individuals and it was concluded that babies born by caesarean section were more likely to be diagnosed with autism or ADHD during the early years of childhood.
Although these associations have a solid scientific level, they have little weight. Children born by caesarean section were 1.33 more likely to be diagnosed with autism and 1.17 more likely to be diagnosed with ADHD.
If we take into account that the prevalence of these diseases is already quite low (about 1% in the case of autism and 7% for ADHD), this increase in probability is not substantial. In the case of autism, this increase in 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 caesarean section.
What does this all mean?
The problem with these types of findings is that It is very tempting to reach 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 seem obvious.
But this simplicity deceives and tells us more about our desire to get simple answers than 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, as well as their causes and how to prevent or manage them.
Epidemiological studies analyze large numbers of population to determine trends in results that indicate the possibility that a given factor coincides with a particular disorder to a greater extent to which it would respond randomly.
In this case there is an observation that people with autism or with ADHD are more likely to have been born by caesarean section than we would normally expect.
But this type of epidemiological study is unable to determine whether one factor (caesarean section) causes another (ADHD or autism).
There are two main reasons:
First, we can't rule out the existence of a third factor That influence this association. For example, we know that cesarean deliveries are more common in obese and older pregnant women, as well as in those with a history of immunological 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 even probable) 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 the mechanism in this field could be the exploration of biological differences in newborns, whether born naturally or by caesarean section, and to understand the way in which these differences may mean an atypical behavior development.
Not having a set of solid evidence from this type of study, simply there is 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 one side and autism and attention deficit hyperactivity disorder on the other. But that is all.
We still don't know why this link exists, but it is almost certain that only cesarean delivery does not contribute to a child's chances of developing autism or ADHD.
In contrast, other pregnancy factors are likely to have 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 of Autism, Telethon Kids Institute, University of Western Australia
This article has originally been published in The Conversation. You can read the original article here.
Translated by Silvestre Urbón
Photos | iStochphoto
