Basal Body Temperature (BBT)
Basal Body Temperature (BBT) is the body's lowest 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 BBT chart.1 A sustained thermal shift on the BBT chart is presumptive evidence that ovulation has occurred but cannot predict ovulation in advance, and a biphasic chart can occur without confirmed ovulation, as in some luteinized unruptured follicle cycles.23 BBT is therefore useful for retrospective evidence of probable ovulation, luteal phase length measurement, and as one signal of possible anovulation when a chart stays monophasic, though some ovulatory cycles also lack a clear thermal shift, so BBT is not reliable as the sole marker for identifying the fertile window.4567
BBT charting requires consistent timing, adequate sleep, and attention to confounders such as illness, alcohol, disturbed sleep, and shift work.2 BBT is a core component of sympto-thermal methods and a secondary confirmatory marker in several other FABMs.89 In restorative evaluation, clinicians integrate BBT charting data with other cycle biomarkers (including cervical fluid and hormonal patterns) to build a full picture of ovulatory function.9
Cited in this entry
- Hilgers TW. The Medical and Surgical Practice of NaProTECHNOLOGY. Pope Paul VI Institute Press; 2004. https://rrmacademy.org/library/the-medical-surgical-practice-of-naprotechnology-rectiyuppdjrktphh/
- Barron ML, Fehring RJ Basal body temperature assessment: is it useful to couples seeking pregnancy?. MCN. The American journal of maternal child nursing. 2005. https://pubmed.ncbi.nlm.nih.gov/16132004/
- Marik J, Hulka J Luteinized unruptured follicle syndrome: a subtle cause of infertility. Fertility and sterility. 1978. https://pubmed.ncbi.nlm.nih.gov/147778/
- Martinez AR, van Hooff MH, Schoute E, van der Meer M, Broekmans FJ, Hompes PG The reliability, acceptability and applications of basal body temperature (BBT) records in the diagnosis and treatment of infertility. European journal of obstetrics, gynecology, and reproductive biology. 1992. https://pubmed.ncbi.nlm.nih.gov/1459325/
- Prior JC, Vigna YM, Schulzer M, Hall JE, Bonen A Determination of luteal phase length by quantitative basal temperature methods: validation against the midcycle LH peak. Clinical and investigative medicine. Medecine clinique et experimentale. 1990. https://pubmed.ncbi.nlm.nih.gov/2364587/
- Bedford JL, Prior JC, Hitchcock CL, Barr SI Detecting evidence of luteal activity by least-squares quantitative basal temperature analysis against urinary progesterone metabolites and the effect of wake-time variability. European journal of obstetrics, gynecology, and reproductive biology. 2009. https://pubmed.ncbi.nlm.nih.gov/19552997/
- Guida M, Tommaselli GA, Palomba S, Pellicano M, Moccia G, Di Carlo C et al. Efficacy of methods for determining ovulation in a natural family planning program. Fertility and sterility. 1999. https://pubmed.ncbi.nlm.nih.gov/10560997/
- Stachowska A, Kicińska AM, Kotulak-Chrząszcz A, Babińska A Usefulness of the Sympto-Thermal Method with Standardized Cervical Mucus Assessment (InVivo Method) for Evaluating the Monthly Cycle in Women with Polycystic Ovary Syndrome (PCOS). Healthcare (Basel, Switzerland). 2024. https://pubmed.ncbi.nlm.nih.gov/38891183/
- Duane M, Stanford JB, Porucznik CA, Vigil P Fertility Awareness-Based Methods for Women's Health and Family Planning. Frontiers in medicine. 2022. https://pubmed.ncbi.nlm.nih.gov/35685421/
Authoritative References
How other clinical authorities define this term. RRM Academy curates these verbatim or under fair use so the medical consensus is visible alongside our RRM-contextualized definition above.
- Wikipedia Basal_body_temperature
Basal body temperature is the lowest body temperature attained during rest. It is usually estimated by a temperature measurement immediately after awakening and before any physical activity has been undertaken.
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