Hormonal mechanisms and the optimal use of luteinizing hormone tests in human menstrual cycle research

Tests of whether women's psychology or behavior shifts during the fertile window vs. other cycle phase regions often employ a design in which fertile window test sessions are scheduled after a positive urinary luteinizing hormone (LH) test result. Lobmaier and Bachofner (2018) point out that this design will schedule high fecundity test sessions at the very end of the fertile window, if not later, when fecundity is not at its highest. I agree with their arguments, and here argue that the problems with this scheduling technique appear even more severe if one considers the hormonal mechanisms that are the likely regulators of cycle phase shifts. Test sessions scheduled after positive LH tests will occur at a time of rapid transitions in hormone production and will often systematically exclude periovulatory days with the highest concentrations of important hormones, such as estradiol. In doing so, this method may often fail to detect cycle phase shifts that are regulated by changes in these hormones. Hypothesis testing in cycle phase research can be improved via a transition from thinking of "fertility" as a discrete and monolithic variable, to instead thinking about the predicted effects of more continuous hormonal signals. I conclude with some general thoughts about how LH tests may be used more productively in studies of cycle phase shifts in psychology and behavior.