Basal body temperature (BBT) is the body temperature measured when the body wakes up after a long period of sleep (more than 6 hours) without any activity, and is the body temperature when the basic vital activity is maintained, also known as resting body temperature. Biphasic temperature curve: The normal basal body temperature is biphasic, i.e. the follicular phase is the low temperature phase and the luteal phase is the high temperature phase. The low temperature phase lasts for about 2 weeks and the high temperature phase lasts for 12-16 days, with an average of about 14 days. From the day of ovulation to the next menstrual day, the body temperature rises by 0.3~0.5℃. Before the temperature rise, there is usually a low point of temperature (some people may have none), and then the temperature rises sharply. This kind of temperature curve which is low before and high after (low before ovulation and high after ovulation) is called biphasic temperature curve and suggests ovulation of the ovaries. Monophasic basal body temperature: The high and low temperature phases cannot be clearly distinguished during the menstrual cycle, which is called monophasic basal body temperature. It indicates poor ovarian function and no ovulation. Checking method: Every night before going to bed, throw the mercury column of the thermometer to below 36℃ and place it at the head of the bed. Immediately after waking up in the morning or after 6 hours of sleep, test the oral temperature for 5 minutes before getting up and before performing any activity. The measured temperature was then recorded on the basal body temperature chart and linked into a curve by day. At the same time, the relevant factors affecting the fluctuation of body temperature, such as sexual life, menstruation, insomnia, cold and fever and medication, etc., will be recorded on the temperature sheet at the same time. Generally, the temperature should be measured for more than 3 consecutive menstrual cycles, and the measurement time should be longer in the case of infertility diagnosis and treatment. Clinical significance: 1. It is difficult to accurately determine the ovulation date, but the basal body temperature can roughly estimate the ovulation date, and the accuracy of predicting ovulation is about 84%. Ovulation usually occurs 1~2 days before the rise of body temperature or during the rise from the low temperature phase to the high temperature phase. Some people have a 0.3~0.5℃ drop in basal body temperature during ovulation, which is due to the high level of estrogen prompting an increase in acetylcholine, causing vasodilation and increasing heat dissipation; some people have no temperature drop. Some scholars found that 5% of ovulation occurs 1 day before the day of minimum body temperature, 22% on the day of minimum body temperature, 40% at the end of low body temperature and 25% on the first day of high body temperature. 2.Guiding conception Sexual intercourse on or within 24 hours before or after the estimated day of ovulation can easily lead to conception. 3.Understand luteal function: Basal body temperature should rise immediately after ovulation, and high temperature should be maintained for 12-16 days, with an average of 14 days; with normal luteal function, the high temperature phase can reach 12 days. Luteal insufficiency: The clinical manifestation is shortened menstrual cycle, or menstrual cycle within the normal range, but the patient is not easy to conceive or miscarriage in early pregnancy. Basal body temperature: biphasic, but the high temperature phase is too short, less than 12 days, especially less than 11 days; or low temperature to high temperature in a “step” slowly rising (more than 3 days); or the rise is low, the rise is less than 0.3 ℃; or basal body temperature is unstable (high temperature phase fluctuations greater than 0.1 ℃); or high temperature end of a small amount of Vaginal bleeding, all suggest luteal insufficiency. Luteal atrophy: prolonged menstrual period. Basal body temperature shows a slow decline in the high temperature phase. The menstrual period is still high-temperature phase body temperature. 4, combined with ultrasound to diagnose luteinization syndrome of unruptured follicles (LUFS): follicular luteinization syndrome refers to the development of mature follicles without ovulation, but granulosa cells undergo luteinization to secrete progesterone, and the basal body temperature is biphasic. The diagnosis of non-ruptured follicular luteinization syndrome can be made by ultrasound detection of follicles that do not become smaller or larger during the hyperthermia period. 5.Diagnosis of early pregnancy: Basal body temperature continues to rise for 16~18 days (without HCG) suggesting possible early pregnancy; over 20 days, early pregnancy can be confirmed. Gradual decrease of basal body temperature during early pregnancy suggests luteal insufficiency and the tendency of miscarriage. 6, indirectly understand ovarian function: in general, biphasic body temperature with ovulation, monophasic body temperature without ovulation, indirectly reflecting ovarian (reserve) function. 7, other: menstrual basal body temperature does not fall, in addition to luteal atrophy incomplete, may also be due to ectopic lesions of endometriosis bleeding after the absorption of heat. Primary amenorrhea with biphasic basal body temperature should be considered uterine type amenorrhea, such as no uterus or tuberculosis destroying the endometrium.