Inaccuracy of basal body temperature charts in predicting urinary luteinizing hormone surges.

Sixty basal body temperature (BBT) charts were reviewed by three reproductive endocrinologists in an attempt retrospectively to predict the urinary luteinizing hormone (LH) surge. LH surges had been previously detected in all cycles with the use of a commercially available monoclonal antibody kit, Ovustick (Monoclonal Antibodies, Inc., Mountain View, CA). Surges were correctly predicted to the day (day 0) 18.3% to 30.0% of the time, to within 1 day on either side of day 0 56.7% to 70.0% of the time, to within 2 days 83.3% to 98.3% of the time, and to within 3 days 96.7% to 98.3% of the time. The BBT remains an inaccurate predictor of the day of the LH surge but does provide a reasonably accurate guide to the 2- to 3-day period on either side of the surge.