Sodium homeostasis in term and preterm neonates. II. Gastrointestinal aspects.

Eighty five 24 hour balance studies were performed on 70 healthy newborn infants of gestational age 27-40 weeks; dietary intake and stool losses of sodium were measured. There was a relation between gastrointestinal sodium absorption and conceptional age (the sum of gestational and postnatal age), whether expressed as absolute stool sodium losses or as the ratio of stool sodium to dietary sodium intake. The stool K:Na ratio rose appreciably with maturation, although stool content of potassium was not greatly increased. These findings suggest that intestinal sodium absorption is inefficient in immature babies and that the degree of malabsorption is inversely related to conceptional age.