Environmental Effects on Women's Reproductive Cycles: Implications for Fertility

At many points within a woman’s reproductive span, it is more normal to have variable menstrual cycles than regular ones. Yet we pathologize women who stray too far from the 28-day norm, naming and medicalizing these states rather than understanding them in the context of age, reproductive state and environment. Psychosocial stress, energy availability and immune challenges are environmental factors that particularly influence cycles across the reproductive span, from ovarian hormones and follicular dynamics, to the lining of the uterus. These effects are largely reversible when these challenges diminish, providing yet more evidence that modulation of the menstrual cycle is functional and adaptive. Numerous lines of research have unequivocally demonstrated that when subject to ecological constraint, the first components of ovarian function to experience suppression are in the luteal phase. Yet the proximate mechanisms that underlie variation in conception, implantation, and thus pregnancy rates, all of which require an understanding of luteal reproductive function, are under-described. Emergent themes in the evolutionary study of women’s reproductive function allow us to explain and promote additional research on the functional modulation of menstrual cycles. This in turn makes it possible to examine unique aspects of human conception, implantation and pregnancy, and more carefully bound definitions of pathology. Examining environmental effects via an inflammatory mechanism offer a new way to understand variation in ovarian hormones, follicular dynamics, and endometrial function.