Perhaps the single feature that most clearly distinguishes the reproductive endocrinology of the female from that of the male is the dependence of female reproductive function on an entirely different set of endocrine rhythms. In considering abnormal female reproductive function, it is imperative to remember what is normal for that moment in the life of that individual.

An overview of the patterns of circulating concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E₂) throughout the life of the normal woman is depicted in Figure 95-1. Rhythmic changes occur in the hormones secreted by all levels of the reproductive system. Moreover, hormonal secretion is modified through several phases of the life cycle.1 Gonadotropin secretion is low in the prepubertal years, increases before and during pubertal development, assumes the characteristic monthly cyclicity of the reproductive years, and finally increases to high levels after the menopause (i.e., the final menstrual period). These changes are both temporally and causally related to simultaneous rhythms in the secretion of ovarian (especially E₂) and hypothalamic (particularly gonadotropin-releasing hormone [GnRH]) hormones. Superimposed on these long-term changes are the shorter-term rhythms that are so important to female reproduction.

Several distinctive rhythms become prominent as a female child progresses to sexual maturity. Female puberty is characterized by the resetting of the classic negative ovarian steroid feedback loop, the establishment of new circadian (24-hour) and ultradian (60- to 90-minute) gonadotropin rhythms, and
the development of a positive estrogen feedback loop controlling the infradian (monthly) rhythm as an interdependent cyclic expression of the gonadotropins and the ovarian steroids.2 Sleep-related increases in gonadotropins and gonadal steroids become evident during puberty and appear to play an important role in pubertal maturation (see Chap. 91).