PHYSIOLOGY OF PAIN IN LABOR

Labour pain is the result of many complex interactions. Although not f ully determined, the pain arises from distension of the lower uterine segment and cervical dilatation. The neural mechanism of labour has so me features similar to other forms of acute pain; nociceptive informat ion is relayed in small A delta and C afferent fibres to the dorsal ho rn of the spinal cord, mediated by neurotransmitters; from there it ma y be involved in the initiation of segmental spinal reflexes or pass t hrough the spinothalamic tract to the brain. Many factors are activate d during labour which may modify the nocioceptive impulse at different stages of its passage. Some of these factors act synergistically to p romote anti-nociception that peaks at delivery.