"Vaginal delivery may be considered a stress-inducing event to which most fetuses are subject. Fetuses born vaginally have higher levels of catecholamines, cortisol and endorphins than those born by elective caesarean section. It is unclear whether this stress response is related to the painful stimulus of head compression or to other factors, such as mild hypoxaemia or maternal stress. In normal labour, this evidence of fetal stress would be considered a normal fetal physiological response and the stress is thought to have benefits for fetal survival. The labour-related surge in steroids and catecholamines is an important factor in activating sodium channels and promoting the clearance of lung fluid. Babies born by caesarean section before the onset of labour have an increased incidence of respiratory complications, such as transient tachypnoea of the newborn. In addition, recent data show that elements of the stress response, perhaps noradrenaline or endorphins, have a short-term analgesic effect, so that babies born vaginally have an attenuated physiological and behavioural response to a painful stimulus compared with those born by elective caesarean section. Evidence of endogenous fetal analgesia during vaginal birth, as well as the role of catecholamines in promoting lung fluid reabsorption and the respiratory depressant actions of fetal opiate exposure, all suggest that the current approach to intrapartum analgesia, centred around maternal, rather than fetal, requirements for pain relief, is the correct one. The evidence that stress responses during normal vaginal delivery have benefits cannot, however, be readily extrapolated to stress responses during pregnancy."