Measure do not guess: a call to action to end assumed and estimated menstrual cycle phases in research

When the prevailing narrative is that female populations have been underserved by research, accepting assumptions and estimates is not the progress it is purported to be. The solution The way to establish menstrual cycle phases in research (ie, laboratory and field-based studies) is clear: in addition to noting regular bleeding, investigators need to measure ovulation and progesterone, noting that the ideal frequency and modality of these measurements are still to be determined. If measurements were not made, it is imperative that authors provide (1) the rationale why measurements were not made; (2) a completely transparent description of the limitations associated with their study design and (3) a full disclosure of the implications of their assumptions and estimations on research quality, confidence in the findings, ability—or rather inability—to make scientific inferences, and the specific clinical dangers associated with assumptions and estimations.