The Basal Body Temperature (BBT) is the temperature of a woman’s body after she has had at least six hours of sleep (also called the "waking temperature").

Changes in the BBT throughout the menstrual cycle (low before ovulation; high after ovulation until menses--"bleeding"), reflect changes in a woman's reproductive hormones. They are related to the event of ovulation (when an egg is released from an ovary). Outside factors such as illness, disturbed sleep, dramatic weight loss, and alcohol consumption can affect the BBT's accuracy in reflecting a woman's reproductive hormonal changes.

When the BBT is used as a method of Natural Family Planning (NFP), a woman takes her temperature at approximately the same time each day under the same conditions. Before ovulation (the pre-ovulatory phase of the menstrual cycle), the temperature remains at a low level. After ovulation has taken place, a rise in the BBT can be seen. The woman records these changes either in a hard copy chart, or electronically in a personal account on a secure website, personal computer, or app.

The BBT can be used as a method of NFP on its own or as a support to the sign of cervical mucus used in the Sympto-Thermal Method (STM) or the Sympto-Hormonal Method (SHM).

To obtain citations of foundational research, see the NFP Science Bibliography.


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Supplemented BBT and Regulation of Conception
Josef Roetzer
This article examines the "Supplemented" Basal Body Temperature Method which includes self-observation of cervical mucus during the preovulatory phase of the menstrual cycle. The results of this study show a high effectiveness rate for pregnancy avoidance.


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