Does basal body temperature occurs before 4 days of menses?

Basal body temperature (BBT) typically rises after ovulation and remains elevated until the onset of menstruation. In the luteal phase, which occurs before menstruation, BBT can remain elevated for about 10 to 16 days. Therefore, it is common for BBT to be elevated in the 4 days leading up to menses, but it does not indicate that menstruation is imminent until it drops just before the period starts.