ABSTRACT. Objective. To document metabolic adaptation to ex utero life in small-(SGA) and large-forgestational-age (LGA) infants in relation to fetal nutrition and postnatal feeding practices.Methods. In a prospective study, 65 SGA (98th centile) full-term infants were recruited. Anthropometry was performed within the first 48 hours. There was full support of breastfeeding and close clinical observation. Blood glucose and ketone body (kb) concentrations were measured prefeed for the first 7 postnatal days. Infants were exclusively breastfed (BF), breastfed with formula milk supplementation (FS), or exclusively formula milk fed (FF).Results. Within the SGA group, a measure of "thinness," the midarm circumference/head circumference ratio, was significantly correlated to the number of episodes of blood glucose <2.00 mmol/L. Epoch (age at sampling) analysis in this group showed no difference in blood glucose levels across the different feeding groups but revealed a statistically significant greater kb concentration for infants who were exclusively breastfed. For SGA infants, the median peak kb concentration (peak kb) was significantly different for BF, FS, and FF groups. Multiple regression analysis for the SGA group demonstrated that peak kb concentration was negatively related to the volume of formula milk, independent of blood glucose levels and neonatal anthropometry. For LGA infants, low blood glucose levels were offset by kb concentrations equivalent to those observed in infants who were appropriate for gestational age.Conclusion. Neonatal ability to generate kb when blood glucose values are low depends more on successful breastfeeding than on size for gestational age or neonatal nutritional status. Routine blood glucose monitoring of LGA infants with no additional risk factors is not necessary. Routine formula milk supplementation for LGA and SGA infants should not be recommended. Pediatrics 2002;109(3). URL: http://www.pediatrics.org/cgi/content/ full/109/3/e42; small for gestational age, large for gestational age, breastfeeding, ketone bodies, hypoglycemia.

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