Changes in basal body temperatures and the prediction of the onset of labor

Pregnant women were requested to chart daily basal body temperatures from the 37th week of gestation until the birth of their infants in order to examine whether changes in basal body temperatures occur in relationship to the spontaneous onset of labor in such a way the labor can thus be predicted. Thirty-five women entered the study, resulting in 3 vaginal temperature and 16 oral temperature charts which met criteria for spontaneous labor. Mean vaginal and oral temperatures did not differ significantly. Charts meeting criteria for spontaneous onset of labor were analyzed for significant changes in basal body temperatures with the cumulative sum (CUSUM) test. Nine charts (47.4%) had erratic patterns with no significant changes in baseline basal body temperatures. Five charts (26.3%) demonstrated a significant drop in temperature 2-6 days (mean=3.4 days) before the onset of labor. Four charts (21.1%) had a significant drop 16-19 days (mean=17.5 days) prior to labor. One chart (5.2%) signalled a drop 30 days before labor. Changes in basal body temperatures observed in these subjects have too much individual variation to support the use of temperature charting and analysis as a tool which can predict the spontaneous onset of labor.