"Data gathered from premature babies on intensive care units suggest that exposure to repeated, strong stimuli can alter cardiovascular responses to a painful stimulus later in infancy and that fetuses born with higher cortisol levels in cord blood, owing to vaginal delivery, have an altered stress response to vaccination. These data suggest that fetal exposure to ‘stress’ in utero can modulate the later function of the hypothalamic pituitary axis. From this, it has been suggested that reducing the magnitude of the initial stress response, for example by using fetal analgesia, will have a beneficial effect. However, the degree to which these effects can be observed following fetal exposure to a painful stimulus remains uncertain, as the majority of studies to date are postnatal and refer to intense, repetitive stimuli that are not normally experienced in utero. The uncertain benefit of attenuating the fetal stress response to a noxious stimulus in utero by administering analgesia needs to be balanced against the practical difficulties to the administration of effective fetal analgesia, as well as the possibility of adverseeffects."