What is "basal body temperature"

n. body temperature in the morning before rising or moving about or eating anything

Basal body temperature (BBT) is the lowest body temperature attained during rest (usually during sleep). It is usually estimated by a temperature measurement immediately after awakening and before any physical activity has been undertaken. This will lead to a somewhat higher value than the true BBT (see Fig. 1). For more accurate results, it is determined by using internally worn temperature loggers. In women, ovulation causes an increase of one-half to one degree Fahrenheit (one-quarter to one-half degree Celsius) in BBT; monitoring of BBTs is one way of estimating the day of ovulation. The tendency of a woman to have lower temperatures before ovulation, and higher temperatures afterwards, is known as a biphasic pattern. Charting of this pattern may be used as a component of fertility awareness. The BBT of men is comparable to the BBT of women in their follicular phase.