A method of recording, storing, analyzing, and displaying changes in a woman's basal body temperature includes the steps of: (a) recording with an intelligent, preprogrammed thermometer the woman's orally-measured temperature; (b) storing in the thermometer the woman's temperature to create a stored temperature reading; (c) repeating steps (a) and (b); (d) analyzing inside the thermometer the significance of any changes in the stored temperature readings; and (e) displaying the changes in the woman's basal body temperature, and displaying an analysis of those changes, on the thermometer, and on any electronic device connected to the thermometer. In other features of the invention, steps (a) and (b) are repeated daily when the woman first awakes from her night's sleep, and the woman first inputs into the thermometer data about herself, including at least her year of birth, her height, her weight, her body mass index, and her current and past menstruation data.