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
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