This is a randomized, controlled trial designed to evaluate a new strategy for promoting continued breastfeeding for mothers and babies who initiated breastfeeding in the newborn period. The new strategy, called Early Limited Formula (ELF), consists of 10mL of formula fed to each baby by syringe after each breastfeeding prior to the onset of mature milk production. The study intervention is discontinued at the onset of mature milk production, and the investigators will then follow mothers and infants for 12 months to assess the effect of ELF on breastfeeding duration, maternal experience and healthcare utilization.