BACKGROUND: In recent years, several reports have indicated that maternal temperature elevations during labor may also be observed in the absence of an infection. Presumed noninfectious causes of maternal temperature elevations include epidural analgesia, endogenous heat production generated by the contracting uterus, and delivery in an overheated room. To investigate the potential causes of noninfectious maternal temperature changes during labor, we conducted a prospective cohort study in women scheduled for labor induction. METHODS: We recorded hourly oral temperatures from admission to delivery. We calculated whether temperature changed during labor in 81 women. We then determined if body mass index, and duration of labor, or time from rupture of amniotic sac to delivery, or oxytocin dose, would affect maternal temperature. To evaluate the possible role of epidural analgesia, we compared the temperature slope before and after starting epidural analgesia. RESULTS: We observed an overall significant linear trend of temperature over time with an estimated temperature slope of +0.017°C/h (P = 0.0093). Patients with a positive temperature trend had also a significantly longer time from rupture of membranes to delivery (P = 0.0077) and a higher body mass index (P = 0.0067). Epidural analgesia had no effect on the temperature trend. CONCLUSIONS: In our cohort of patients, there was an overall significant linear trend of temperature over time after correcting for heterogeneity among patients. Temperature increase was associated with higher body mass index values and longer time from rupture of membranes to delivery. Epidural analgesia had no effect on maternal temperature. Copyright © 2012, the American Society of Anesthesiologists, Inc. Lippincott.