Recent methodological recommendations suggest the use of the "3-step method," consisting of calendar-based counting, urinary ovulation testing, and serum blood sampling, for the identification of subtle menstrual disturbances (SMDs). However, the use of the 3-step method is not always feasible, so a less demanding combination of calendar-based counting and urinary ovulation testing, that is, the 2-step method, may be a viable alternative. Purpose To investigate the agreement between the 2- and 3-step methods for the detection of SMDs. Methods Menstrual cycles (MCs, 98) of 59 athletes were assessed using the 2- and 3-step methods. Regular-length MCs (ie, =21 and =35 d) were classified as either having no SMD (luteal phase length =10 d, midluteal progesterone concentration =16 nmol·L-1, and being ovulatory) or having an SMD (eg, short luteal phase [<10 d], inadequate luteal phase [midluteal progesterone concentration <16 nmol·L-1], or being anovulatory). Method agreement was assessed using the McNemar test and Cohen kappa (k). Results Substantial agreement was observed between methods (k = .72; 95% CI, .53-.91), but the 2-step method did not detect all MCs with an SMD, resulting in evidence of systematic bias (x2 = 5.14; P = .023). The 2-step method detected 61.1% of MCs that had an SMD ([51.4, 70.8]), as verified using the 3-step method, and correctly identified 100% of MCs without an SMD. Conclusions MCs classified as being disturbed using the 2-step method could be considered valid evidence of SMDs. However, MCs classified without SMDs do not definitively confirm their absence, due to the proven underdetection via the 2-step method.
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