Basal body temperature is a commonly used non-invasive method to monitor ovulation. It is a measurement of the body temperature in the resting state of the body, which is taken after more than 6 hours of adequate sleep and before any activity after waking up. Its fluctuation can indirectly reflect the ovarian function of a woman. If the basal body temperature changes in the high temperature phase, it means that ovulation may have occurred and a change in treatment should be sought from the doctor in time. Therefore, learning to read the basal body temperature is very important for patients with polycystic ovary syndrome who are taking herbal medicine, not using contraception or other patients with poor ovulatory function. Liu Xinmin, Department of Gynecology, Guang’anmen Hospital, Chinese Academy of Traditional Chinese Medicine Basal body temperature is not a straight line, but fluctuates from high to low. In women with normal ovulation function, the body temperature is slightly lower in the first half of the menstrual cycle, a condition called low temperature phase; in the second half of the menstrual cycle, i.e. after ovulation, the body temperature increases by 0.3 to 0.5℃, a condition called high temperature phase. The high-temperature phase lasts for about two weeks and then drops to the original level 1 to 2 days before menstruation or on the first day of menstruation. This cyclical change in body temperature is called biphasic temperature (Figure 1). The basal body temperature rises from 3 days before to 1 day after ovulation, and if you have sex without contraception, you have a higher chance of getting pregnant. If the body temperature does not rise significantly, but fluctuates up and down at a certain level, it means no ovulation, and this temperature is called monophasic temperature (Figure 2). If the basal body temperature rises for more than 18 days, there is a high probability of pregnancy (Figure 3) and the urine pregnancy test should be checked promptly. Once early pregnancy is diagnosed, patients with polycystic ovary syndrome should have their blood HCG and progesterone checked as soon as possible to determine timely fertility control measures. In addition, fever caused by cold and certain special conditions may affect the basal body temperature, so special conditions should be marked in the thermometer. Basal body temperature is a good reference to determine whether ovulation is occurring and to guide the use of medication, so it is important to bring it to the clinic. Please refer to my article “How to get a number” for more information about registration.