In mammals, birth is one of the most biologically complex processes for both the woman and the fetus. Indeed, a complex hormonal network is set up to allow delivery, while the fetus must, at birth, quickly adjust its metabolic, hormonal, pulmonary, cardiovascular, immunological, and microbiotic functions to allow its survival. The conditions under which this process takes place can be the source of many neurological and psychiatric diseases, hence the importance of determining the mechanisms. Birth mode – vaginally or by cesarean section – is also an important factor. Thus, the number of births by cesarean section is constantly growing, with an average world rate of 18.6%, 20% in France, and more than 50% in Brazil, Egypt and Dominican Republic. These changes are related to a social evolution of the perception of cesarean sections, associated with an increase in the number of cesareans scheduled without a medical reason. However, the epidemiological data on the neurological and psychiatric sequele occurring after a term or pre-term planned cesarean are discussed. For most of these studies, cesareans increase the incidence of autism. To date, the largest study, conducted on 5 million births in the Nordic countries and Australia, suggests an increase in the incidence of autism, whether cesarean section is performed at term or pre-term. This problem remains complex because of the heterogeneous conditions associated with cesarean birth. This is why experimental data in controlled conditions are essential to understand the real link between cesarean section and autism.
In a study conducted in Marseille (Luminy) by Morgane Chiesa as part of her thesis project, on the direction of Yehezkel Ben-Ari and with the support of the Neurochlore team, the effects of the planned caesarean section on neuronal development have been studied in mice. Caesareans were performed either at term or 24 hours before the term (longer delays were impossible because of the immaturity of the lungs). We compared different anatomical, physiological and cellular criteria in newborns from birth to adulthood. The results suggest that caesarean sections, whether performed at term or pre-term, do not impact the electrical activity of neurons or the behavior of mice in adulthood. However, in pups born pre-term by caesarean section, neurons are transiently underdeveloped at birth and an increase in vocalization behavior is observed.
These data suggest that caesarean term does not induce harmful consequences for the fetus. However, a pre-term cesarean induces transient alterations that, cumulative to a problem occurring during pregnancy, during or shortly after birth, could lead to long-term sequelae.