Body composition of the preterm infant.

The body composition of 23 infants was examined at postmortem. All infants were live births and lived from 1 to 192 days. Their body weights at birth ranged from 480 to 3280 g; gestational ages ranged from 24 to 42 weeks. Total body composition was determined using the nondestructive in-situ procedures of 40K counting and neutron activation analysis. The absolute amounts of K, Ca, P, Na, and Cl were measured. Although body Cl was in general agreement with estimates for the reference fetus model, body K and Na values were lower. Body Ca content was higher than the reference fetus at body weights above 2 kg, yet body P levels agreed with the reference fetus. Furthermore, those infants whose survival was brief had reduced body K, an index of body cell mass. All elements except body Cl were linearly related to fat-free mass (FFM). The correlations with gestational age were non-significant when the variation in elemental content was accounted for by FFM or body weight. The two preterm infants who survived for more than 10 weeks had significantly reduced bone growth as shown by their Ca and P deficiences.