Under normal circumstances, a woman’s basal body temperature is low after menstruation and during the follicular phase, while after ovulation, due to hormonal changes in the body, so the body temperature will slightly increase. That is, the rise in temperature usually means that ovulation has occurred. The following is an analysis of both the cause and the significance: 1. After ovulation due to the formation of the corpus luteum in the ovary, the progesterone produced by the corpus luteum can stimulate the hypothalamus thermoregulatory center, which raises the body temperature by about 0.5°C. This state lasts for 14-16 days, until 1-2 days before menstruation or the first day after the onset of menstruation, when the body temperature drops. Therefore, an increase in body temperature indicates that ovulation has occurred; 2. Significance: Due to this change in body temperature during ovulation, clinical gynecology often applies the basal body temperature measurement to understand the ovarian function of women, to see if ovulation has occurred, to estimate the ovulation date and to monitor the luteal function of the ovaries. This is done by taking the sublingual temperature in the morning after waking up and recording it, and then plotting it on a basal body temperature graph. If the woman’s body temperature has risen by about 0.5°C, she has ovulated. If the woman is fertile and has recently had intercourse, close observation of temperature changes is recommended. If the temperature rises and does not drop for about 3 weeks and there is no menstruation, pregnancy is considered and a blood HCG test is recommended to further clarify if she is pregnant.