Babies coming into the world by cesarean section experience epigenetic changes, a study has found. So far there has not been enough follow up to know whether the effects are long lasting, but the discovery may explain the relatively poorer outcomes for babies delivered in this way.

Cesarean delivery, where the mother's abdomen and uterus are surgically cut open to remove the baby, was once a last, desperate option. However, rates are increasing dramatically worldwide, closing on 50% in China.

The trend is deeply controversial among health professionals, with a variety of concerns expressed about the consequences, including hemorrhaging, persistent pain and depression for the mother and respiratory diseases and obesity for the baby. However, in many countries perverse financial incentives favor the use of cesareans even where a vaginal birth is probably the better choice.

Despite epidemiological evidence that cesarean birth is associated with a higher risk of conditions such as type-1 diabetes the mechanism is unknown, which may have hampered responses. However, Professor Tomas Ekstrom has provided a step towards an explanation with a paper in the American Journal of Obstetrics and Gynecology.

"In this study, our focus has been whether the way a baby is born can have an impact on a cellular level in the form of epigenetic alterations in DNA,” Ekstrom said.

Ekstrom found higher rates of methylation in stem cells from 18 babies delivered by by cesarean than 25 via vaginal birth. Methylation of DNA affects whether genes are expressed or not within a cell and is the major path through which environmental factors can alter the expression of genetic traits.

When Ekstrom did a more detailed study of twelve of the babies he found statistically significant differences in methylation in almost 350 regions, many of which are known to influence the immune system.

"During a vaginal delivery, the fetus is exposed to an increased level of stress, which in a positive way will prepare the unborn baby for life outside the uterus," said co-author Professor Mikael Norman. "This activation of the fetus' defense systems doesn't occur when a cesarean section is performed before labor begins, which in turn could be a possible cause for the noticed differences between the groups.”

“"The biological mechanisms predisposing a fetus or a newborn infant to get a certain disease later in life are complex and depend on both genetic and environmental factors during formative years", Ekstrom noted. He pointed out that epigenetic changes can be either temporary or permanent and it is too early to tell whether the effects he identified will last. However, it is particularly concerning that some epigenetic effects are not only permanent, but get passed on to offspring, potentially making the effects of a single birth multigenerational.