Background: An objective method of menstrual cycle tracking while minimizing participant burden and cost for field-based research is needed. A modification was proposed to a well-known three-step (m3-step) method to improve accessibility for participants and athletes with difficult travel schedules. Methods: A longitudinal design was employed, and the m3-step method (calendar counting, urinary ovulation, and salivary hormones) was completed over three consecutive cycles to assess performance while classifying menstrual variability. Naturally cycling females (N=28; age 18-36 years) from across Canada were recruited prospectively. Participants shipped their hormone samples to the lab where they were classified as "high" or "low" hormone based on ovulation status and a progesterone/estradiol (P4/E2) ratio of 100 pg/mL. Cycle length (mean, ±; SD) was self-reported (28.9 ± 4.16 days) and salivary testing occurred on cycle day 22.5 ± 3.26. Results: The average luteinizing hormone surge for those with a positive test occurred on cycle day 14.2 ± 2.27 (22/28). Average cycle length (t (24.1) = 2.44, p = 0.02), progesterone (t (21.1) = -4.72, p < 0.01) and P4/E2 ratios (t (18.9) = -7.74, p < 0.01) were statistically significant between high (12/28) and low (16/28) hormone groups. A logistic regression explored the relationship of progesterone to the hormone classification criteria using a crudes odd ratio (1.98 (95% CI 1.24 - 3.17, p < 0.01)). Conclusion: The m3-step method yielded a sensitivity of 65% and specificity of 91% using the P4/E2 ratio of 100 pg/mL. Limitations included self-reported naturally cycling, the day of the testing and the P4/E2 value used. In summary, this study examined the feasibility of a m3-step menstrual cycle tracking method to classify hormones as high or low in naturally cycling females for potential implementation in a field-based setting.
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