THURSDAY, July 2, 2009 (HealthDay News) -- Babies delivered by cesarean section experience changes to the DNA of white blood cells, which might explain why they're at increased risk for immunological diseases such as diabetes and asthma later in life, Swedish researchers say.
"Delivery by C-section has been associated with increased allergy, diabetes and leukemia risks," Dr. Mikael Norman, a pediatric specialist at the Karolinska Institute in Stockholm, said in a news release from Wiley-Blackwell publishers. "Although the underlying cause is unknown, our theory is that altered birth conditions could cause a genetic imprint in the immune cells that could play a role later in life."
Norman and his colleagues analyzed blood samples from 37 infants taken just after delivery and samples taken three to five days after birth. The blood was analyzed to assess the degree of DNA-methylation in the white blood cells, which are a key part of the immune system. In DNA-methylation, DNA is chemically modified to activate or turn off genes in response to changes in the external environment.
The 16 infants born by C-section had higher DNA-methylation rates immediately after delivery than the 21 infants born by vaginal delivery, according to the report, in the July issue of Acta Paediatrica. Three to five days after birth, both groups of infants had similar levels of DNA-methylation.
Further research is needed to determine why infants born by C-section have higher DNA-methylation rates after delivery, the researchers said.
"Animal studies have shown that negative stress around birth affects methylation of the genes, and therefore it is reasonable to believe that the differences in DNA-methylation that we found in human infants are linked to differences in birth stress," the researchers wrote.
"We know that the stress of being born is fundamentally different after planned C-section compared to normal vaginal delivery," they explained. "When babies are delivered by C-section, they are unprepared for the birth and can become more stressed after delivery than before. This is different [from] a normal vaginal delivery, where the stress gradually builds up before the actual birth, helping the baby to start breathing and quickly adapt to the new environment outside the womb."
The Nemours Foundation has more about cesarean delivery.