Basal body temperature as method of natural family planning

Basal Body Termperature

• basal body temperature (BBT) elevation retrospectively identifies fertility
• luteinizing hormone surge, which stimulates ovulation, is associated with a 0.5- to 1°F- (0.9- to 1.8°C) rise in BBT measured with highly standardized methods (1)
• BBT can be taken orally, vaginally, or rectally with a sensitive thermometer
  • same site should be used daily
• BBT
  • measured on awakening at approximately the same time every morning, before getting out of bed or doing any other activity
    • at least 6 hours of uninterrupted sleep the preceding night is necessary for accurate measurement
  • remains elevated throughout the luteal phase secondary to higher progesterone levels
  • woman assumed to have ovulated after observing 3 consecutive days of temperature elevation
  • pregnancy is avoided by abstaining from the beginning of menstruation until 3 to 4 days after the rise in BBT
    • all subsequent days until the beginning of her next menses are considered infertile
      • because sperm survive 5 days, BBT alone does not predict ovulation far enough in advance to identify all the potentially fertile days; it predicts only peak fertility, so thus the need to abstain from the beginning of menstruation (1)
  • many other factors also limit the use of BBT
    • some women ovulate without a clear rise in BBT
    • inaccurate basal temperature measurement can be caused by alcohol consumption, late nights or oversleeping, disrupted sleep, travel, time zone differences, holidays, shift work, stress, illness, gynecologic disorders and medications
    • biphasic shift of BBT has been found to vary up to 1 day before and 3 days after actual ovulation

Reference:

• 1) Pallone SR, Bergus GR.Fertility awareness-based methods: another option for family planning. J Am Board Fam Med. 2009 Mar-Apr;22(2):147-57.
• 2) Evans C.Natural family planning is effective and culturally acceptable.BMJ. 2012 Jul 23;345
• 3) Freundl G et al.State-of-the-art of non-hormonal methods of contraception: IV. Natural family planning. Eur J Contracept Reprod Health Care. 2010 Apr;15(2):113-23