Menstrual Phase Identification Questionnaire (MPIQ): Development and validation of a cross-sectional survey to identify follicular and luteal phases.

Evidence continues to accumulate on the influence of the menstrual phase on several biobehavioral outcomes (e.g., substance misuse). Expansion of this knowledge is limited due to the burdensomeness of accurate menstrual phase assessment. Thus, we sought to create and validate a questionnaire that can be used as a stand-alone item within low-resource settings and numerous study designs (e.g., cross-sectional) to accurately identify both the follicular phase (FP) and the luteal phase (LP). Participants completed the self-administered four-item Menstrual Phase Identification Questionnaire (MPIQ) in two recently completed clinical trials. We assessed the accuracy of two MPIQ scoring criteria (less restrictive and more restrictive), as compared to self-report of onset of menses alone, with progesterone confirmation via dried blood spots. Participants (n = 59) were, on average, 33.7 (standard deviation [SD]: ± 4.3) years old and provided a total of 83 responses. Assessing FP and LP using the self-reported onset of menses alone classified 65.1% of the responses with an overall phase identification accuracy of 60.2%. While the more restrictive MPIQ scoring classified 100% of the responses, it yielded a similar accuracy (68.4%). In contrast, the less restrictive MPIQ scoring classified 100% of the responses and also significantly improved phase identification accuracy to 92.1% (p < .001). The MPIQ, as a stand-alone item, allows all cross-sectional responses to be classified with a high level of accuracy. This low-burden questionnaire can be used alone to identify FP and LP in studies that may be otherwise limited by study design, finances, and/or participant burden. (PsycInfo Database Record (c) 2024 APA, all rights reserved).