All infants lose weight after they are born, no matter what or how they are fed. However, there are conflicting opinions about what constitutes a normal newborn weight loss, especially in exclusively-breastfed infants, and about when interventions, such as supplemental feedings, should be considered. This review will: Present evidence for the amount and timing of initial weight loss and timing of birth weight recovery. Explain the normal physiology of the newborn infant in the early days of life. Determine whether intrapartum intravenous (IV) fluids cause excessive weight loss in some newborn infants. Present information which should allow health professionals to make an informed assessment of what is contributing to an individual newborn infant's weight loss.