The Accuracy of Standardized Methods for Assigning Menstrual Cycle Phase in Young Women

While measurement of daily sex hormone levels is the preferred method to capture phases of the menstrual cycle, these studies are expensive and labor intensive. A common practice in research is the use of self-reported menstrual cycle (MC) date to subsequently categorize the MC into pre- or post-ovulatory phases. PURPOSE: To determine if self-reported MC data can be used to accurately categorize women with regard to MC phase using standard cut-offs reported in the literature. METHODS: As part of a larger study, 73 recreationally active women [age range: 18-30 yrs], completed a one page questionnaire on MC history previously validated by Wojtys et al. (1998). In addition, women returned to the lab between 0630-0900 hr for 6 days during menses and for at least 8 days after a positive urinary ovulation test (luteal phase) for 2 consecutive MC [C1 and C2]. All blood samples were collected at the same time of day±30 minutes for each subject and were assayed for progesterone (P=ng/ml). Standard methods relying only on MC days for phase determination were utilized as cut-offs and compared to the phase determined from P concentration and the positive urinary ovulation test. All analyses were completed using SAS. RESULTS: Counting 10-14 days from the onset of menses (often used to define ovulation), captured a positive urinary ovulation test (UOT) in only 35% and 42% of the cases in C1 and C2, respectively. Counting back 12-14 days from the projected start date of the next cycle captured the positive UOT in only 32% and 23% of the cases in C1 and C2, respectively. In 71% of cases, the criterion hormone value for ovulation [P>2.0 ng/ml], was obtained >14 days after the onset of menses. The most accurate standard method for capturing ovulation hormone values [criteria; P>2.0 ng/ml], was counting forward 1-3 days from a positive UOT, which captured 78% of all cases. All the standard methods for capturing mid-luteal hormone values [criteria; P>4.5 ng/ml], produced equal results and were effective 67% of the time. CONCLUSION: When daily hormone measures to determine MC phase are not feasible, the combination of self-reported data and a positive UOT is the most accurate method for determining MC phase. However, caution should be used with these methods since nearly 25-30% of all women have variation in the MC that will result in improper phase determinations.