The menstrual cycle is regular, with each cycle lasting 28-30 days. Ovulation usually occurs about 14 days before the next menstrual period. The 10 days between 5 days before and 4 days after ovulation is the ovulation period, which is also the fertile period. The basal body temperature before ovulation in the menstrual cycle is often low, with a normal daily temperature of 37°C or less, around 36.4°C-36.6°C, upon waking up early in the morning. The body temperature drops slightly during ovulation and rises on average by about 0.5℃ after ovulation, maintaining it until just before the onset of menstruation when it starts to drop and then returns to its original temperature level. The body temperature during ovulation is variable. Under normal circumstances, a woman’s basal body temperature is low before ovulation and rises after ovulation because the corpus luteum formed when the ovaries ovulate and the secretion of more progesterone stimulate the hypothalamic thermoregulatory center, causing the basal body temperature to rise.