This study reports the temporal pattern of milk output in 2 groups of lactating mothers during the first 6 weeks postpartum. A study aim was to examine if the average milk output for postpartum days 6 and 7 (baseline) predicts milk adequacy at week 6 postpartum. Mothers of preterm (< or = 31 weeks) infants (n = 95) used mechanical expression to initiate and maintain their milk supply; mothers of a singleton healthy term infant (n = 98) fed their infant at the breast. Baseline milk output was predictive of milk adequacy, defined as > or = 500 mL/d at week 6 (P = .000). Preterm mothers were 2.81 times more at risk of not producing adequately than term mothers were. Study findings suggest that interventions that promote the initiation and maintenance of an adequate milk supply during the first week postbirth are critical.