Planned caesarean births—”C-sections”—slightly raise the risk of some childhood cancers—particularly acute lymphoblastic leukemia (ALL), a fast-growing cancer of the blood and bone marrow.
This is the conclusion of a study by researchers at Sweden’s Karolinska Institutet, which analyzed health records from nearly 2.5 million children born between 1982 and 2015.
The findings indicate that children born by planned C-section—those scheduled before labor begins—appear to have a 21 percent higher risk of developing ALL compared to those born vaginally.
The risk was even higher—29 percent—for the most common subtype, B-cell ALL (B-ALL). While the researchers stress that the overall risk remains low, the study offers new insight into the potential long-term impacts of elective surgical births.
“C-sections are an important and often life-saving part of obstetric care [and] we don’t want mothers to feel anxious about medically indicated C-sections,” said lead author Christina-Evmorfia Kampitsi, a researcher at the Institute of Environmental Medicine at Karolinska Institutet.
But when combined with other studies linking planned C-sections to asthma, allergies and type 1 diabetes, it’s worth discussing non-medically indicated procedures, she added.
Using Sweden’s national birth and cancer registries, the team identified 1,495 children later diagnosed with leukemia.
Children born via emergency C-section—typically after labor has already begun—did not show the same elevated risk.
The researchers suggest this may be because emergency deliveries expose infants to natural stress hormones and maternal vaginal bacteria, which play a role in immune system development.
In contrast, planned C-sections—often performed before labor begins—bypass these natural exposures, potentially affecting how the infant’s immune system matures.
The elevated risk appeared more pronounced in boys and younger children, although the researchers caution that some results did not reach full statistical significance.
Still, they argue the findings are meaningful, especially given that previous research has pointed to similar links.
Kampitsi said that fortunately, acute lymphoblastic leukemia is rare. As a result, a large number of C-deliveries are required to achieve statistical significance, which presents challenges in collecting such a substantial sample size in a Swedish registry study.
“However, the results are close to significant, are in line with what previous studies have shown, and remain when we adjust for other relevant factors, which still makes them relevant,” she said.
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Reference
Kampitsi, C.-E., Mogensen, H., Heyman, M., Feychting, M., & Tettamanti, G. (2025). Mode of delivery and the risk of lymphoblastic leukaemia during childhood – A Swedish population-based cohort study. International Journal of Cancer. https://doi.org/10.1002/ijc.70027
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