Basal Body Temperature
In its daily rhythm, the human body is subject to periodic temperature fluctuations. During sleep, a temperature minimum is established in the body core, which is called basal body temperature (BBT). In practice, the core body temperature upon waking is often referred to as the BBT.
The basal body temperature in the first half of the cycle (at the beginning of the period until ovulation) is about 36.6 °C. Shortly after ovulation, the temperature rises by at least 0.2 °C and is also slightly elevated on the following days.