Basal Body Temperature (BBT)
Basal Body Temperature (BBT) is the body's resting temperature, measured orally or vaginally first thing in the morning after at least three hours of uninterrupted sleep and before any activity, eating, or drinking. BBT rises 0.2 to 0.5 degrees C within one to three days after ovulation due to the thermogenic effect of progesterone released by the corpus luteum; this sustained shift produces a characteristic biphasic pattern on a cycle chart.1 A thermal shift confirms that ovulation has occurred but cannot predict ovulation in advance. BBT is therefore useful for retrospective ovulation confirmation, luteal phase length measurement, and detection of anovulation, but is not reliable as the sole marker for identifying the fertile window. Accuracy depends on consistent timing, adequate sleep, and the absence of confounders (illness, alcohol, disturbed sleep, shift work). BBT is a core component of sympto-thermal methods and a secondary confirmatory marker in several other FABMs.
Cited in this entry
- Hilgers TW. The Medical and Surgical Practice of NaProTECHNOLOGY. https://rrmacademy.org/library/the-medical-surgical-practice-of-naprotechnology-rectiyuppdjrktphh/
Discussed in
Research library
- Basal body temperature graph and the luteal phase defect
- Natural family planning. II. Basal body temperature and estimated time of ovulation
- Basal body temperature assessment: is it useful to couples seeking pregnancy?
- The effect of personal factors on the use of the basal body temperature method of regulating births
- Monitoring of ovarian activity by measurement of urinary excretion rates using the Ovarian Monitor, Part IV: the relationship of the pregnanediol glucuronide threshold to basal body temperature and cervical mucus as markers for the beginning of the post-ovulatory infertile period
Patient questions
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