Temporal relationship between basal body temperature nadir and luteinizing hormone surge in normal women.

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.