Postnatal weight loss in term infants: what is "normal" and do growth charts allow for it?

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Abstract
Background: Although it is a well known phenomenon, limited normative data on neonatal weight loss and subsequent gain are available, making it hard to assess individual children with prolonged weight loss. Objective: To establish, using data from a large prospective population based cohort study, norms and limits for postnatal weight loss and its impact on current growth reference charts. Method: A cohort of 961 term infants were recruited at birth and followed using parental questionnaires and community nursing returns. Routine weights were collected for half the cohort at 5 days and for all at 12 days and 6 weeks. Results: Less weight loss was seen than the 3–6% suggested by previous studies, but one in five infants had not regained their birth weight by 12 days. Those lightest at birth showed least weight loss. Twenty six (3%) children had more than 10% weight loss, but none showed evidence of major organic disease. Actual weights in the first fortnight are half to one centile space lower than growth charts suggest, while birthweight centiles for children born at 37 weeks were two centile spaces lower. Conclusions: Neonatal weight loss is brief, with few children remaining more than 10% below birth weight after 5 days. Growth charts are misleading in the first 2 weeks, because they make no allowance for neonatal weight loss.