A New Study Uncovers a Concerning Connection Between Cesarean Deliveries and Infant Leukemia Rates

In Sweden, almost one in six children is born today by Cesarean, a large part of which is scheduled without medical emergency. If this practice is often perceived as safe and comfortable, recent research suggests that it is not devoid of long -term consequences for the health of the child. A vast study by Karolinska Institutet and published in July 2025 in The International Journal of Cancer reveals a worrying link between planned cesarean births and an increased risk of acute lymphoblastic leukemia (LL), the most common form of pediatric cancer.

A robust methodology and a crucial distinction between the types of cesareans

The study is based on the richness of Swedish national registers, renowned for their precision and their exhaustiveness. By crossing the data from the medical register of births with those of the cancer register, the researchers were able to reliably trace the medical history of each child. Including the circumstances of birth. A determining element was the ability to differentiate the cesareans programmed in advance – carried out before the start of work – of those decided in emergency during childbirth. This distinction made it possible to better understand the proper effect of the planned cesarean.

To strengthen the validity of the results, the team excluded children with congenital malformations or known genetic disorders to increase the risk of leukemia. It has also taken into account several socio -demographic variables. Namely: level of education of parents, gestational age, birth weight, birth rank or maternal smoking during pregnancy. This rigorous statistical adjustment work limits potential biases.

The researchers also verified whether the observed link was found for other types of child's cancer. No excess risk has been identified for brain tumors or lymphomas, thus strengthening the specificity of the association between planned cesarean and LAL. This coherent data bundle suggests that the delivery method could interfere with early mechanisms linked to immune development, especially in the very first days of life.

Understand the mechanisms at stake, a disturbed immune development track

The researchers advance several hypotheses to explain the link between planned cesarean and increased risk of acute lymphoblastic leukemia (LL). One of the most studied concerns the role of the microbiota. As a reminder, it is all the microorganisms that naturally colonize the human body from birth. During a childhood by low way or even an emergency cesarean, the child is exposed to vaginal and intestinal bacteria of his mother. This first microbial contact plays an essential role in activating and balanced the immune system.

However, a planned cesarean, carried out before the start of work, prevents this exhibition. The newborn is then colonized differently, often by bacteria of environmental or hospital origin. This interaction deficit with the maternal microbiota could permanently modify how the immune system learns to recognize what is dangerous or not. According to Christina-Evmorfia Kampitsi, this early alteration could affect certain immune regulation mechanisms. She adds that this could open the way to inappropriate reactions. Including the development of abnormal cells that cause cancers like the LAL.

A second factor mentioned is the absence of physiological stress linked to childbirth. This moderate stress is caused by contractions and the passage in the vaginal channel. He triggers in children the release of hormones like cortisol. These hormones would play a key role in maturing immune and metabolic functions. In the absence of this signal, certain crucial cell development stages could be disrupted.

These mechanisms, still poorly understood, call for additional research. However, they reinforce the idea that a planned childbirth without medical reason could modify fundamental biological processes from the first hours of life.

Excess modest risk, but scientifically confirmed

The link observed between planned cesarean and acute lymphoblastic leukemia (LL) remains modest on an individual level. But it is statistically significant at the scale of a population. The LAL-B, the most common form of infantile leukemia, remains a rare disease. In Sweden, each year has been recorded between 50 and 70 new cases. It is estimated to increase the risk associated with a birth by Cesarean section scheduled for 29 % for the LAL-B. Concretely: only one additional case approximately per 100,000 births per year.

This means that, for a given child, the risk remains very low. But when you consider an entire population, this excess becomes quantifiable. As Professor Giorgio Tettamanti, co-author of the study, points out, ” It takes several hundred thousand cesareans to observe a statistically significant elevation ». This observation does not detract from the validity of the results. He simply recalls that the child's cancers are rare, which makes epidemiological studies more complex.

Certain sub-analyzes do not reach the conventional threshold of statistical significance, often set at a 95 %confidence interval. This does not imply that there is no link, but rather that the results must be interpreted with caution. However, the interest of this study is precisely due to convergence with other previous works carried out in different countries. This consistency between several studies strengthens the credibility of the observed association.

Towards a more demanding reflection on the programmed cesareans

This study opens up a sensitive but necessary debate: that of the growing use of cesareans planned without medical reason. The researchers remind us with clarity: the Cesareanus constitutes a saving intervention in many obstetric contexts. It is therefore not a question of questioning its legitimacy when it is medically justified. But, as Kampitsi indicates, ” What we call into question are the convenience cesareans, practiced without clinical necessity ».

This positioning joins a broader awareness on the long -term impacts of birth conditions. Other studies have already established links between the programmed cesarean and an increase in the risk of asthma, allergies or diabetes of type 1.. Adding an increased risk of acute lymphoblastic leukemia, even low, reinforces the urgency of reassessing the non -medical indications of this intervention.

Beyond the question of the method of childbirth, these results contribute to a better understanding of the possible origins of the LL. They show that the first hours of life – and the biological processes that are triggered there – can weigh on the development of the immune system in a lasting way. It is a still young research field, but deep implications for public health.

The authors hope that these results will serve as the basis for future international studies. By questioning our earliest medical choices, it invites us to collectively rethink what is comfort and what is prevention.

Source: Kampitsi CE, Mogensen H, Heyman M, Feychting M, Tettamanti G. “Mode of Delivery and the Risk of Lymphoblastic Leukemia During Childhood-Swedish Population-Based Cohort Study”. Int j cancer. 2025; 1-8.