A prospective multicentre study to develop universal immunochemical tests for predicting the fertile period in women. World Health Organisation Task Force on Methods for the Determination of the Fertile Period, Special Programme of Research, Development and Research Training in Human Reproduction.

Two immunochemical tests for predicting the fertile period have been adapted for application throughout the world. The estrone test involves the measurement of estrone-3-glucuronide (E1-3-G) in daily samples of early morning urine. The start of the fertile period is identified by a sustained rise in the concentration of E1-3-G (as determined by cumulative sum analysis); the end of potential fertility occurs 120 hours (5 days) after the peak level. Alternatively, the ratio of E1-3-G to pregnanediol-3 alpha-glucuronide (Pd-3 alpha-G) can be calculated and the fertile period identified between a defined rise in this index and the peak value plus 144 hours (6 days). One hundred thirty-one women from 10 countries provided samples from 557 menstrual cycles, and the results from 455 (82%) were accepted for statistical analysis. There were highly significant differences (P less than 0.0001) in the concentrations of the metabolites between centres, but the time intervals between both the rise and peak days and the day of the luteinizing hormone (LH) peak were less significantly different (P less than 0.05) for the estrone test and not significantly different for the ratio test. The fertile period was defined as the day of the LH peak -3 to the day of the LH peak +2. The estrone test successfully delineated this phase in 78% of menstrual cycles, and the ratio test, in 74%. The mean lengths of the derived fertile periods by both methods were 9.3 (SD 2.3) and 10.0 (SD 2.4) 24-hour periods (or days), respectively.