A large Swedish study on 2.4 million births reveals that children born by planned cesarean present 21% additional risks to develop acute lymphoblastic leukemia, the most common cancer in children. This research, published in the International Journal of Cancer, confirms and specifies previous observations while raising crucial questions about the biological mechanisms at stake at birth. Although absolute risk remains low, this discovery challenges the long -term consequences of certain obstetric practices.
A disturbing statistical link
Acute lymphoblastic leukemia (LL) mainly affects children under the age of five, representing around 80% of pediatric leukemia. Despite its relative rarity – only 4.8 in 100,000 children develop it each year – it constitutes a major concern in pediatric oncology.
The team of Christina Evmorfia-Kampitsi of Karolinska Institutet analyzed two decades of Swedish data with unequaled precision. Of the 2.4 million births studied, around 375,000 children were born by cesarean, including 213,000 per planned cesarean. Among the entire cohort, 1,200 children have developed a LAL.
The results reveal a significant increase in risk in children born by planned cesarean-that is to say programmed before the start of work-compared to vaginal delivery. This temporal distinction turns out to be crucial: unplanned cesareans, made after the start of work, show a lower risk increase.
Methodological rigor makes the difference
This study is distinguished by its rigorous control of confusing factors. Researchers have taken into account maternal age, birth weight, congenital malformations, gestational diabetes, preeclampsia and many other variables likely to influence the results.
This methodological approach responds to criticisms formulated against previous studies, often accused of not sufficiently distinguishing the direct effects of the Cesarean from pathologies that have motivated this intervention. “” Thanks to the wealth of data from the Swedish register, we have been able to demonstrate that this association is not only due to the underlying conditions“, Explique Evmorfia-kampitsi.
The subdivision by decade of birth also makes it possible to take into account the evolution of obstetric practices and diagnostic techniques, strengthening the robustness of the conclusions.
Credit: ISTOCK
Authority of cancer cells in the blood flow. Credits: Nemes Laszlo/Istock
Two plausible biological mechanisms
How to explain this surprising link? Scientists advance two complementary hypotheses, both linked to the fundamental differences between vaginal and planned cesarean birth.
The first theory, known as “microbial”, suggests that exposure to microorganisms of the vaginal canal plays a protective role. During a vaginal childbirth, the newborn comes into contact with the maternal flora, stimulating its immune system early. This microbial “education” could promote the elimination of pre-leukemic cells present from birth.
Babies born by planned cesarean, having never crossed the vaginal canal, would be deprived of this crucial exhibition. Even the Césareans made after breaking of the waters pocket offer superior microbial exposure, which could explain their intermediate risk.
The second hypothesis concerns stress hormones. The work generates a massive release of cortisol and other stress hormones in the fetus. These substances, far from being harmful, could activate anti -cancer defense mechanisms. This theory finds an echo in the therapeutic use of corticosteroids to treat the LL.
A relative risk in an absolute reassuring context
Joseph Wiemels, expert in cancer epidemiology at the University of Southern California, tempers the legitimate concern that these results can arouse. Although the increase in relative risk is statistically significant, the absolute risk remains low.
Concretely, out of 100,000 children born vaginal, about 4.8 will develop leukemia. This figure increases to approximately 5.8 for children born by planned cesarean. The absolute increase therefore remains marginal, even if it becomes significant at the population level.
Measured clinical implications
The authors insist on a fundamental point: these results should not dissuade the use of the cesarean when it is medically justified. Severe preeclampsia, fetal distress, abnormal presentation or other obstetric complications constitute absolute indications where profits largely prevail over risks.
« Cesarean section is an essential and often saving element of modern obstetric care“, Recalls Evmorfia-Kampitsi. “Our results should not be a source of concern when the procedure is medically indicated. »»
On the other hand, this discovery could influence decisions concerning cesareans of convenience, practiced without clear medical indication. In these situations, the benefit-risk balance could now integrate this long-term oncological consideration.
Towards new research
This Swedish study, despite its robustness, calls confirmations in other populations. Geographical variations in cesarean and LAL levels suggest that environmental or genetic factors could modulate this association.
The identification of precise mechanisms also opens up fascinating preventive perspectives: microbial supplementation of newborns by cesarean, optimization of the timing of interventions, or development of protocols mimicking the benefits of physiological work.
This research perfectly illustrates how modern epidemiology can reveal subtle but significant links, guiding the evolution of medical practices towards an ever thinner consideration of the long -term consequences of our interventions.