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Principle, Method, and Curve Analysis of Basal Body Temperature

Principle of basal body temperature

Basal body temperature refers to the body temperature during a state of rest, which reflects the energy metabolism level of the body at rest. After ovulation, the corpus luteum in women produces progesterone, which can affect the temperature regulation center in the hypothalamus and increase the basal body temperature by 0.3-0.5℃, which lasts until 1-2 days before the menstrual period or the first day of menstruation. After that, the temperature returns to its original level. Therefore, in a normal menstrual cycle with ovulation, the daily measured basal body temperature can be plotted as a double-sided curve, while if there is no ovulation, the basal body temperature remains unchanged and forms a single-phase curve.

Method of measuring basal body temperature

Before going to bed every night, shake the mercury column of the smart basal thermometer to below 36℃, place it within reach, and do not speak or move after waking up the next morning. Place the family care thermometer under the tongue and measure the oral temperature for 5 minutes. The measurement time should be fixed and recorded on the basal body temperature chart, and the results should be connected to form a curve. If there are any factors that affect body temperature such as menstruation, sexual activity, insomnia, cold medication, etc., they should be noted on the chart to facilitate better interpretation.

Typical basal body temperature curve

In women of childbearing age with normal ovarian function, the basal body temperature has its own regular curve pattern. In the first half of the menstrual cycle (follicular phase), the basal body temperature fluctuates at a low level (around 36.5℃). During the ovulatory phase, it slightly decreases or may not be obvious, and then rises into the second half (luteal phase), generally increasing by 0.3-0.5℃ to around 36.8-37℃, and maintaining that level until the menstrual period or 1-2 days before. The temperature then drops back to its original level. The length of the menstrual cycle mainly depends on the length of the follicular phase, and the length of the luteal phase is usually around 14 days.

Mastering the ovulatory phase can guide contraception. It is generally believed that ovulation may occur within about 2-3 days before the increase in basal body temperature, and during the period from 4 days after the temperature rise to before the menstrual period, even with sexual activity, it is generally safe from pregnancy, and is considered a safe period. From the end of the menstrual period to 3 days before the increase in basal body temperature is the relatively safe period. At this time, it is only possible to predict when the temperature will rise, and there is no exact time. Moreover, sperm can survive in the female reproductive tract for 2-3 days, so the safe period may not be very safe. However, by measuring the basal body temperature for multiple menstrual cycles and mastering its curve pattern, a general plan can be made for contraception. The range of the ovulatory phase is 2-3 days before and after the rise in basal body temperature, and sexual activity during this period is most likely to result in pregnancy, which is the fertile period. Women who plan to conceive can have sex during this period.

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