Basal body temperature (BBT) as a predictor of ovulation was assessed by examining the temporal relationship between the BBT shift and the luteinizing hormone (LH) surge in individual cycles of 27 normal women. For 22 of the subjects, the LH surge occurred on the same day or within one day of the BBT nadir. For the remaining five subjects, the surge fell within 2 days after or 3 days before the nadir. Despite the BBT nadir's close temporal association with the LH surge, daily examination of BBT for the purpose of predicting the day of ovulation during a given cycle is unsatisfactory. By 48 hours following the nadir, when one could usually be certain that temperature elevation had occurred, all subjects had already exhibited the LH surge.
PIP: The basal body temperature (BBT) as a predictor of ovulation was evaluated by determining the time relationship between BBT shift and the serum luteinzing hormone (LH) surge. Individual menstrual cycles of 27 women (median age, 25 years) were studied. BBTs were recorded each morning. Blood samples were taken for 10-14 consecutive midcycle days. In all subjects, the peak LH level on the day of the surge was more than 4 times the mean level for the follicular and luteal phases of the cycle. For 22 of the 27 subjects (81%), the LH surge occurred on the same day or within 1 day of the BBT low point. For 5 subjects, the surge fell within 2 days after or 3 days before the nadir of BBT. The day of the BBT shift could not be located in 12 of 43 subjects originally tested. When the shift was obvious 48 hours or more were sometimes needed to be sure it had occurred. By this time the LH surge would have occurred and the subjects would have been partly or completely through the period of maximum fertility. For either fostering conception or preventing pregnancy, BBT is considered an unsatisfactory signal.