AIM:To assess how maternal/infant characteristics and early hospital practices influenced exclusive breastfeeding at 2-3 weeks postpartum among mothers intending to breastfeed their late preterm and early term infants. METHODS:This secondary analysis used data from a randomised controlled trial of 72 mothers of late preterm (34 + 0-36 + 6) and early term infants (37 + 0-38 + 6), assigned to either a breastfeeding intervention or control group. Information on hospital practices and infant feeding was collected prior to intervention start. RESULTS:Overall, 62% of infants were exclusively breastfed (57% of late preterm, 75% of early term infants) at 2-3 weeks postpartum. In-hospital formula supplementation was highly prevalent (76%), and particularly larger volumes (30-60 mL per feed) were strongly associated with reduced exclusive breastfeeding (p < 0.001). Being offered support for breastfeeding problems at hospital was also associated with reduced odds of exclusive breastfeeding (OR 0.17, 95% CI 0.04-0.84). Early hospital practices, such as skin-to-skin contact and early breastfeeding initiation, differed between early term and late preterm infants. CONCLUSIONS:The findings highlight the potential impact of modifiable hospital practices, particularly formula supplementation, on exclusive breastfeeding in this group. Strategies to improve these practices warrant further investigation. TRIAL REGISTRATION:ClinicalTrials.gov identifier: NCT03791749.