The optimization of an immunochemical test to locate the fertile period in women

Abstract

An immunochemical test, for predicting the limits of the fertile period and the time of maximum potential fertility in women, has been optimized by application to 118 menstrual cycles from apparently healthy women. The test is based upon changes in the concentration of oestrone-3-glucuronide (E₁-3-G) in daily samples of early morning urine (EMU). Two rises (R₁ and R₂) above a mean background level are determined by CUSUM analysis to give signals 72 hours and 24 hours before the time of the LH peak, or maximum follicular diameter (in 38 cycles). Subsequently, a peak level of E₁-3-G is identified and the end of potential fertility is calculated. The optimum number of days to determine the baseline, the appropriate reference levels to detect rise days 1 and 2, and the minimum number of days from the peak, have been studied in relation to the length of the derived fertile period. Under optimum conditions the test for the start and end of potential fertility was successful in 95% of cycles, and the mean length of the fertile period was 10.2 days (SD ± 2.7). The best test for maximum potential fertility gave a signal in 95% of cycles, with a mean time of 43 hours to the time of maximum follicular diameter. Eighty-two per cent of the signals occurred within the range + 48 hours to - 24 hours.