Background: Early in the COVID-19 pandemic, many birth hospitals separated SARS-CoV-2-positive mothers from their newborn infants and advised against breastfeeding to decrease postnatal SARS-CoV-2 transmission. Information on how these practices impacted breastfeeding postdischarge is limited. Objectives: In a statewide sample of SARS-CoV-2-positive mothers, we aimed to determine the extent to which (1) mother-infant separation and (2) a lack of breastfeeding initiation in-hospital were associated with breast milk feeding postdischarge. Design/Methods: From 11 birthing hospitals in Massachusetts, we identified 187 women who tested positive for SARS-CoV-2 from 14 days before to 72 hours after delivery (March 1-July 31, 2020) and their newborn infants. We abstracted chart data from the delivery hospitalization on main exposure variables (mother-infant separation, in-hospital breast milk feeding [expressed milk feeding and/or direct breastfeeding]) and from outpatient visits until 30 days postdischarge. We evaluated associations of in-hospital practices with outcomes up to 30 days postdischarge, adjusting for confounders using multivariable logistic and linear regression. Results: Mother-infant separation in-hospital was associated with a shorter duration of any breast milk feeding (regression coefficient estimate -5.29 days, 95% confidence intervals [CI] [-8.89 to -1.69]). Direct breastfeeding in-hospital was associated with higher odds of any breast milk feeding (adjusted odds ratios [AOR] 5.68, 95% CI [1.65-23.63]) and direct breastfeeding (AOR 8.19, 95% CI [2.99-24.91]) postdischarge; results were similar for any breast milk feeding in-hospital. Conclusions: Perinatal hospital care practices implemented early in the COVID-19 pandemic, specifically mother-infant separation and prevention of breast milk feeding initiation, were associated with adverse effects on breast milk feeding outcomes assessed up to 1 month postdischarge.