A Method for Estimating the Day of Ovulation by Basal Body Temperature Chart

The method for estimating the day of ovulation by the basal body temperature fluctuation was studied and appraised. The temperature variation within 0.1°C above or below the mean basal body temperature of the first 10 menstrual days was defined as the hypothermic phasic range. When the basal body temperature rose and remained above hypothermic phase for 4 consequtive days, it is considered to have shifted into the hyperthermic phase and the day before a shift into the hyperthermic phase was estimated as the day of ovulation. Continuous measurement of urinary LH concentrations from early morning samples established the LH peak day. The accuracy of this method was examined by comparing the basal body temperature and urinary LH peak. In 36 cycles (69%) BBT fell within two days around when the ovulation was most likely to occur, and fell within 2 days before and after the LH peak in 46 cycles (88%). A slight scattering in the estimates was due to the influence of factors other than progesterone on the basal body temperature. This seems as insurmountable limit to using basal body temperature for this purpose. In absence of any other means than BBT to estimate the day of ovulation, our simple objective method is quite practical and useful.