Children born by planned C-section have an increased risk of developing acute lymphoblastic leukaemia (ALL) later in life. This is shown by a study conducted by researchers at Karolinska Institutet. The researchers emphasise that the risk remains low.
The study, published in The International Journal of Cancer, covers nearly 2.5 million children born in Sweden during two periods, 1982 to 1989 and 1999 to 2015. Of these, 15.5 per cent were born by C-section, i.e. nearly 376,000 children. In the entire group, 1,495 children later developed leukaemia.
Using the Medical Birth Register, the researchers were able to divide the C-sections into planned and emergency caesarean sections. The children who later developed leukaemia were overrepresented in the group born by planned C-section. In particular, the risk of the most common form of childhood leukaemia, acute lymphoblastic leukaemia (ALL), increased. The risk of ALL was 21 per cent higher in children born by planned C-section compared with children born vaginally.
Risk is higher in boys than girls
The risk of developing the most common form of ALL, B-cell acute lymphoblastic leukaemia (B-ALL), was 29 per cent higher in those born by planned C-section. The increased risk remained even when the researchers adjusted for other relevant factors in mothers and children. The increased risk was more pronounced in boys than in girls and among younger children.
The researchers emphasise that the risk remains low, regardless of the mode of delivery. Between 50 and 70 Swedish children per year are diagnosed with B-ALL. The excess risk associated with planned C-sections corresponds to approximately one case of B-ALL per year, according to the researchers behind the study.
"C-sections are an important and often life-saving part of obstetric care. We don't want mothers to feel anxious about medically indicated C-sections. But when this result is combined with other study results showing that the risk of later asthma, allergies or type 1 diabetes increases in children born by planned C-section, there is reason to discuss C-sections that are not medically indicated," says Christina-Evmorfia Kampitsi , researcher at the Institute of Environmental Medicine , Karolinska Institutet, and lead author of the study.
The researchers discuss possible mechanisms that could explain why it is planned and not emergency C-sections that carry an increased risk of certain diseases, all of which are related to immunological factors. The reasoning is that emergency caesarean sections usually begin as a vaginal delivery. This causes stress for the baby and exposure to vaginal bacteria if the amniotic sac has ruptured.
Stress and vaginal bacteria may explain difference
However, in planned C-sections, which are usually performed before labour has started naturally, the baby does not experience this stress and is not exposed to vaginal bacteria. The researchers suggest that this difference may help explain the increased risk of ALL, and believe that the study may contribute to a better understanding of what causes ALL in children.
Some of the results did not reach the threshold for statistical significance, meaning that chance cannot be entirely ruled out.
"Fortunately, ALL is rare. This means that many C-deliveries are needed to obtain a statistically significant result, and it is difficult to obtain such a large sample 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," says Christina-Evmorfia Kampitsi.
The research is funded by the Swedish Research Council and the Swedish Cancer Society. The researchers state that there are no conflicts of interest.
Publication
"Mode of delivery and the risk of lymphoblastic leukaemia during childhood - a Swedish population-based cohort study", Christina-Evmorfia Kampitsi, Hanna Mogensen, Mats Heyman, Maria Feychting, Giorgio Tettamanti, The International Journal of Cancer, online July 4, 2025, doi: 10.1002/ijc.70027
