It is usually estimated by a temperature measurement immediately after awakening and before any physical activity has been undertaken.
[2] The higher levels of estrogen present during the pre-ovulatory (follicular) phase of the menstrual cycle lower BBTs.
The higher levels of progesterone released by the corpus luteum after ovulation raise BBTs.
There is limited evidence about the effectiveness of fertility awareness family planning methods, some of which use basal body temperature as one component.
Records of basal body temperature can be used to accurately determine if a woman is ovulating.