A study conducted in China found that babies who are born through a difficult birth involving forceps are more likely to develop behavioural problems than those born through Caesarean section. The relationship, they suggest, is explained by cortisol response.

Cortisol is a hormone produced by the body when it is under stress. Previous studies have found that the cortisol levels found in umbilical cord blood are lowest in babies born through elective Caesarean section, even lower than those born naturally through spontaneous vaginal delivery. The highest level were found in those born through assisted vaginal delivery—using forceps—or vacuum extraction.

Professor Jianmeng Liu, the lead researcher, explained that studies have linked cortisol levels to childhood psychopathology, but added that further research is needed to better understand this phenomenon.

The researchers assessed 4,190 children from China’s southern provinces, aged 4-6. They found that children born through assisted vaginal delivery were most likely to exhibit behavioural traits such as depression, attention difficulty, delinquency, aggression, anxiety and being withdrawn.

In China, the number of Caesarean births is on the rise, especially in the wealthier southern parts of the country. In these areas, the rate of Caesarean births has gone from 22% in 1994 to 56% in 2006. A major contributor to this is the number of requests for Caesarean delivery, which increased from 3.6% to 36% between the same years.