Neonatal weight loss in breast and formula fed infants.

OBJECTIVE To define the range of neonatal weight loss in a population relative to feeding method. DESIGN Prospective observational cohort study. SETTING Maternity service providing geographically defined, community based newborn follow up. PARTICIPANTS 971 consecutive term newborns of birth weight > or = 2500 g during the first 2-3 weeks of life; 34 excluded (inadequate data). 937 included: 45% breast fed, 42% formula fed, 13% breast and formula fed. OUTCOME MEASURES Maximum weight loss and timing, age on regaining birth weight. RESULTS Median weight loss: formula fed 3.5%, breast fed 6.6%. Upper centiles for maximum weight loss differ considerably (95th centiles: breast fed = 11.8%, formula fed = 8.4%; 97.5th centiles: breast fed = 12.8%, formula fed = 9.5%). Median time of maximum weight loss: 2.7 days for breast fed and formula fed. Recovery of birth weight: breast fed median 8.3 days, 95th centile 18.7 days, 97.5th centile 21.0 days; formula fed median 6.5 days, 95th centile 14.5 days, 97.5th centile 16.7 days. The time taken to regain birth weight correlates with both the degree and timing of initial weight loss for all groups. CONCLUSIONS Early neonatal weight loss is defined allowing identification of infants who merit closer assessment and support.