A child’s risk of leukemia may be shaped by whether labor occurs before delivery, a new study suggests.
Babies born by planned cesarean section face a modestly increased risk of developing leukemia, according to a Swedish study of more than 2.4 million births.
The research, published in The International Journal of Cancer, found that those born via scheduled C-section—before labor begins—were about 20 percent more likely to develop acute lymphoblastic leukemia (ALL), the most common type of childhood leukemia, compared with children born vaginally or by emergency C-section.
The findings carry particular relevance as cesarean rates climb worldwide. While Sweden maintains relatively low C-section rates of 11 percent to 17 percent, more than 30 percent of babies in the United States are now delivered surgically—and about half of those are scheduled procedures, rather than emergencies.
Key Findings
Researchers analyzed more than 2.4 million births in Sweden across two periods: 1982 to 1989 and 1999 to 2014. Using national health registers, researchers tracked delivery methods and childhood leukemia diagnoses through age 20. Of the 2.4 million births studied, 15.5 percent were delivered by C-section.
The most striking result was a 29 percent higher risk of B-cell acute lymphoblastic leukemia (B-ALL)—the most common subtype—among children delivered by planned C-section, compared with those born vaginally. The association was strongest among boys and children diagnosed before age 5—the peak age for ALL onset.
No such increase was seen in children delivered by emergency or unplanned cesareans, which typically take place after labor begins or in response to complications.
“We were a little surprised that the association persisted after adjusting for a wide range of maternal, pregnancy, and infant conditions,” Christina-Evmorfia Kampitsi, a postdoctoral researcher at the Karolinska Institute and the study’s lead author, said in an email to The Epoch Times.
ALL, including its most common subtype B-ALL, affects white blood cells and is typically diagnosed in children under 5. It is considered highly treatable, with survival rates above 85 percent in high-income countries.
Understanding the Risk
The increase in risk, though statistically significant, is small in absolute terms.
In the United States, approximately 3,100 children and adolescents under age 20 are diagnosed with ALL each year, or about 4 in every 100,000 children. The 20 percent increase observed for ALL would raise that number to about 5 in 100,000.
“The overall risk remains very low—most children born by C-section will never develop leukemia,” Kampitsi said, noting that the team initially suspected that the higher risk might be due to health problems that would have led to scheduling a C-section. Now, it appears the delivery method itself—how the baby is born—may affect immune development in a way that increases leukemia risk.
To assess whether pregnancy complications might explain the link, the researchers adjusted for a broad range of maternal and perinatal factors, including gestational diabetes, preeclampsia, birth weight, maternal age, smoking, and infections. The association still held.
“While we can’t draw firm conclusions [because the study is observational], the findings support the idea that early-life exposures (even as early as birth) may have long-term implications for immune development and immune-related health outcomes,” Kampitsi said.
How Birth May Shape Immunity
Scientists increasingly point to the “wisdom of nature” in the birth process—a finely tuned sequence of events over millennia that helps prepare a newborn’s immune system for life outside the womb.
When labor begins naturally and babies pass through the birth canal, they are exposed to a cascade of biological signals and microbes that appear to play a role in long-term health. Researchers believe two key factors may help explain the link between planned cesareans and an increased risk of childhood leukemia.
Microbiota Exposure
Babies born vaginally are exposed to beneficial bacteria from the mother’s birth canal, which helps populate the infant gut and support early immune regulation. In contrast, babies born by scheduled C-section—before labor and without contact with vaginal flora—are typically colonized by skin and hospital bacteria, which may result in less microbial diversity. This differs from emergency C-sections, where labor has started or after the amniotic membrane has ruptured (water breaking), potentially allowing some exposure to vaginal microbes.
“This difference could potentially influence immune regulation in early life,” Kampitsi stated.
A 2020 study in Science Translational Medicine found that babies born by C-section miss out on the early transfer of beneficial microbes from the mother’s birth canal—an interruption that researchers linked to a higher risk of immune-related conditions like asthma.
Stress Hormones at Birth
Labor triggers a surge of stress hormones, such as cortisol and adrenaline, that help prepare a newborn’s immune system. Babies born via emergency cesarean or vaginally still experience this hormonal spike. However, those delivered by planned C-section, before labor begins, typically do not.
Kampitsi said that stress hormones released during labor may help the newborn’s immune system develop properly and clear out early abnormal cells that could lead to leukemia.
While these mechanisms are biologically plausible, they remain speculative and require further study, she added.
The American College of Obstetricians and Gynecologists notes that cesarean delivery, as well as factors such as antibiotic use and formula feeding, can disrupt the natural transfer of a mother’s bacteria during a critical window of newborn immune development—potentially affecting gut health and long-term immune regulation.
Putting the Risk in Perspective
The findings, which add to growing evidence that the way a baby is born may shape the developing immune system in subtle but lasting ways, align with prior research linking scheduled cesareans to small but measurable increases in asthma, Type 1 diabetes, allergies, and other immune-related conditions.
Most babies born by planned C-section will never develop leukemia, and in many cases, a C-section is medically necessary and lifesaving.
“In such cases, not performing a C-section could result in serious harm to both mother and child,” Kampitsi said.
Still, the study suggests that when a planned cesarean is being considered without a clear medical indication, it’s worth weighing potential long-term risks—however small.
Taken together, the potential long-term effects may be worth discussing with a doctor when there’s no clear medical reason for scheduling a C-section.
