 Several mechanisms have been postulated with no study reaching a conclusion. The mechanisms suggested include imbalance between heat production and heat dissipation, effect of opioid on interleukin-2, markers of inflammation induced by epidural analgesia, etc. Our study aims at the first mechanism. It may be a physiological process that leads to an imbalance between heat production and heat dissipation. Labor is a hyper metabolic state and increased heat production is dissipated via increased ventilation that is associated with labor pains with no epidural pain relief. It is conceivable that laboring women with pain relief subsequent to epidural analgesia, a decrease in ventilations may occur leading to decreased heat dissipation. 