ObjectivesTo examine whether use of expressed human milk in the first two weeks postpartum is associated with cessation of human milk feeding and non-exclusive human milk feeding up to 6 months.DesignPooled data from two prospective cohort studiesSettingThree Canada Prenatal Nutrition Program (CPNP) sites serving vulnerable families in Toronto, Canada.Participants337 registered CPNP clients enrolled prenatally from 2017 to 2020; 315 (93%) were retained to 6 months postpartum. Exclusions: pregnancy loss or participation in prior related study; Study B: preterm birth (<34 weeks); plan to move outside Toronto; not intending to feed human milk; hospitalisation of mother or baby at 2 weeks postpartum.Primary and secondary outcome measuresMain exposure variable: any use of expressed human milk at 2 weeks postpartum. Outcomes: cessation of human milk feeding by 6 months; non-exclusive human milk feeding to 4 months and 6 months postpartum.ResultsAll participants initiated human milk feeding and 80% continued for 6 months. Exclusive human milk feeding was practiced postdischarge to 4 months by 28% and to 6 months by 16%. At 2 weeks postpartum, 34% reported use of expressed human milk. Any use of expressed human milk at 2 weeks was associated with cessation of human milk feeding before 6 months postpartum (aOR 2.66; 95% CI 1.41 to 5.05) and with non-exclusive human milk feeding to 4 months (aOR 2.19; 95% CI 1.16 to 4.14) and 6 months (aOR 3.65; 95% CI 1.50 to 8.84).Trial registration numbersNCT03400605, NCT03589963.