Basal body temperature as a method of ovulation detection: comparison with ultrasonographical findings.

In 47 cycles with hormonal evidence of ovulation, the detection and timing of ovulation by basal body temperature (BBT) and by ultrasonographical observation are compared. The ovulation detection rate by ultrasonographical method proves to be considerably higher than by BBT criteria. The timing of the day of ovulation is evaluated, assuming that the ultrasonographical event of follicle disappearance represents ovulation. BBT criteria nadir, coverline and the eye-balling method show a very poor frequency distribution. The result of the FDHP method is a nearly symmetrical distribution, however, with a considerable range. We conclude that ovulation detection and timing by BBT are not reliable.