The adjustment of basal body temperature measurements to allow for time of waking.

Abstract

During one menstrual cycle, each of eleven volunteer student nurses at Northwick Park Hospital recorded their vaginal temperature on waking and noted the clock time. Waking times varied between 0530 hours and 1100 hours. Regression analysis revealed significant linear relation between temperature and time of waking, with a slope of 0.086 degrees C/hour (SE, 0.009 degrees C/hr) in the postmenstrual (hypothermal) phase. A rounded adjustment factor of 0.1 degrees C/hour is shown to improve the interpretability of basal body temperature (BBT) charts in a group of seven women regularly using natural family planning methods. The adjustment factor is simple to apply and only involves counting one square on a BBT chart for each hour that the waking time differs from normal.