BACKGROUND:To date, there has not been an investigation to determine whether lactating women and their infants influence the ovarian function of other women with whom they interact.

METHODS:In a randomized, double-blind, placebo-controlled study of 47 nulliparous women, we utilized both within- and between-subjects controls to assess the effects of sustained exposure to breastfeeding compounds on menstrual cycle length, as well as characteristics of each phase of the ovarian cycle.

RESULTS:Breastfeeding compounds modulated ovarian cycle length in comparison with the carrier control (0.01

CONCLUSIONS:Because compounds from lactating women and their infants modulated the ovarian cycles of women, as is seen in other mammals, they have the potential to function as pheromones, regulating fertility within groups of women.