The tendency for women to be less fertile when they are lactating. The operational term here is “less fertile,” as breast feeding is not an effective birth control for most women.
Suppression of normal cyclic hormonal changes resulting from breastfeeding. The advent of postpartum ovulation and menses is related to the amount of time the mother breastfeeds. Even after the resumption of menses, 50% of initial cycles are anovulatory. Women who stop nursing within 30 days usually experience the return of menstruation between 6 and 10 weeks after delivery; among those who continue to nurse, ovulation usually occurs between postpartum weeks 17 and 28, with menstruation 30 to 36 weeks after the birth.