of lactation. Because the focus of this report is on healthy women, the discussion omits the influence of lactation on underlying chronic disease states, such as diabetes mellitus, cardiovascular disease, and cystic fibrosis. The discussion is subdivided into two sections: short-term effects (return of ovulation and maternal sexuality) and long-term effects (obesity, osteoporosis, and breast cancer). The effects of breastfeeding on maternal nutritional status are considered in Chapter 9.
Lactation has long been known to increase the length of time between the delivery of a baby and return of regular ovulation. Despite considerable research on this subject, the mechanisms by which lactation exerts this effect on ovarian activity remain incompletely understood (see review by McNeilly et al. ). There is general agreement that suckling suppresses the pulsatile release of gonadotropin-releasing hormone from the hypothalamus and also stimulates the release of prolactin. Gonadotropin-releasing hormone is necessary for the pulsatile release of luteinizing hormone from the pituitary. Luteinizing hormone, in turn, is essential for maturation of the ovarian follicle and, thus, for ovulation. Any direct role prolactin might have in modifying ovarian function remains unresolved.
The characteristics of suckling by the infant appear to be the principal factors that affect the duration of postpartum anovulation (the period of functional importance) or amenorrhea (the length of time that is usually measured) in well-nourished lactating women (McNeilly et al., 1985). Frequency, intensity, and timing of suckling sessions all appear to influence the endocrinologic responses that modulate ovulatory status. These nursing characteristics change as lactation progresses, especially at the time solid foods are added to the infant's diet (Howie et al., 1981).
Maternal nutritional status during lactation may also be an important factor in regulating the duration of postpartum amenorrhea. Observational data show a clear association between poor maternal nutritional status and prolonged postpartum amenorrhea accompanied by persistently elevated prolactin values (see, for example, Hennart et al. ). However, interpretation of this association is not straightforward because there also are differences in suckling characteristics between the infants of well and poorly nourished women.
Several mechanisms have been proposed for the effect of maternal nutritional status on the duration of postpartum amenorrhea. Frisch (1978) hypothesized that a critical proportion of body fat is necessary for the return of normal ovarian function after delivery. Another idea is that the hormonal status that is characteristic of women with chronically inadequate food intake