Caesarean delivery increases risk of childhood asthma

It is thought that the genetic changes that occur when a baby is born by Caesarean section could make them more susceptible to immunological diseases such as diabetes and asthma in later life.

Blood from the umbilical cords of 37 newborn infants was sampled and analysed just after delivery and then three to five days after the birth to assess the DNA-methylation in the white blood cells – a vital part of the immune system. The 16 C-section babies exhibited higher DNA-methylation rates immediately after delivery than the 21 born by vaginal delivery. Three to five days after birth there were no longer significant differences between the two groups.

Delivery by C-section has been associated with increased allergy, diabetes and leukaemia risks. Although the underlying cause is unknown, Professor Mikael Norman, of the Karolinska Institutet in Stockholm theorises that altered birth conditions could cause a genetic imprint in the immune cells that could play a role later in life. This is why the group was anxious 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.

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 found in human infants are linked to differences in birth stress. The stress of being born is fundamentally different after planned C-section compared to normal vaginal delivery. In a C-section, the babies are unprepared for the birth and can become more stressed after delivery than before. In a normal vaginal delivery 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 authors point out that the surgical procedure itself may play a role in DNA-methylation and that factors other than the delivery method need to be explored in more detail. However, in the study, neonatal DNA-methylation did not correlate to the age of the mother, length of labour, birth weight and neonatal CPR levels - proteins that provide a key marker for inflammation; nor was there was any relation between DNA-methylation and these factors.

Although it remains unknown how specific gene expression is affected after C-section deliveries, or to what extent genetic differences related to the mode of delivery are long-lasting, the researchers believe that their findings open up a new area of important clinical research.

Schlinzig et al. Epigenetic modulation at birth Acta Paediatrica, 2009; 98

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First Published in Febuary 2009

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