Factors related to duration of postpartum amenorrhoea among USA women with prolonged lactation.

Duration of postpartum amenorrhoea (PPA) was compared among women who breast-fed for > or = 6 months (breast-feeding group) or < or = 3 months (formula-feeding group) and was found to be significantly shorter among the latter. Associations between maternal factors and duration of PPA were examined. Within the formula-feeding group, the only variable associated with duration of PPA was duration of breast-feeding. Among breast-feeding mothers who resumed menstruation after 3 months postpartum, duration of PPA was positively associated with parity and negatively associated with maternal body mass index (BMI) at 3 months postpartum. Among breast-feeding mothers who resumed menstruation after 6 months, duration of PPA was positively associated with parity, pregnancy weight gain, number of night feeds and milk volume at 6 months, and negatively associated with maternal age and BMI at 6 months postpartum. These results indicate that maternal anthropometric status is related to duration of PPA, even in a relatively well-nourished population of lactating women.