Basal Body Temperature (or BBT) is defined as the lowest natural, non-pathologic body temperature recorded after a period of rest. It is your base temperature at rest, usually reached during deep sleep. Typically, BBT is measured first thing in the morning before you get out of bed.
BBT is a major fertility indicator to help you identify which phase of your menstrual cycle you are in. Your BBT is affected by the hormones that are present in your body, depending on the phase of your cycle. When it is measured daily, these slight changes in temperature can be observed and used to identify pre and post-ovulation phases.
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