A team of Swedish researchers from the Karolinska Institute in Stockholm, Sweden took blood samples from the umbilical cords of 37 newborn infants just after delivery and collected new samples between three and five days following birth. They analyzed the samples to examine the degree of DNA-methylation, or chemical altering of the DNA, in the white blood cells - cells that are a key part of the immune system. Compared to the 21 babies born vaginally, the investigators found higher DNA-methylation rates in the samples taken immediately following the birth of the 16 C-section babies. Those levels dropped within three to five days after birth to the point that there was no longer any significant difference between the two groups.

Scientists believe that these genetic changes, which differ from normal deliveries, could be the reason why people delivered by C-section are more susceptible to immunological diseases such as diabetes and asthma in later life, when those genetic changes combine with environmental triggers. "Delivery by C-section has been associated with increased allergy, diabetes and leukemia risks" says Professor Mikael Norman, who specializes in pediatrics at the Karolinska Institute. "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. That is why we were keen to look at DNA-methylation, which is an important biological mechanism in which the DNA is chemically modified to activate or shut down genes in response to changes in the external environment. As the diseases that tend to be more common in people delivered by C-section are connected with the immune system, we decided to focus our research on early DNA changes to the white blood cells."

Although more research is necessary to determine exactly why the DNA-methylation rates were higher after Caesarean deliveries, the researchers believe there may be a possible connection to altered stress levels. As the authors note, "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. We know that the stress of being born is fundamentally different after planned C-section compared to normal vaginal delivery. 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 to 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."

News Release: Researchers link Caesarean section births to genetic changes http://www.monstersandcritics.com/news/health/news/article_1487933.php/Researchers_link_Caesarean_section_births_to_genetic_changes July 6, 2009

News Release: C-section births cause genetic changes that may increase odds for developing diseases later on in life http://www.sciencedaily.com/releases/2009/06/090629081443.htm June 29, 2009