Altered body composition in preterm infants at hospital discharge

To test the hypotheses that body size is reduced and body composition altered in preterm infants at hospital discharge.

Preterm infants (< or = 34 weeks gestation, < or = 1750 g at birth) were enrolled. Body weight, length and head circumference were converted to standard deviation or z-scores. Body composition was measured using dual emission X-ray absorptiometry. The results were analysed using standard statistics.

One hundred and forty-nine infants (birth weight = 1406 +/- 248 g, gestation = 31 +/- 1.7 weeks) were studied. Postmenstrual age at discharge was 37 +/- 1.2 weeks. Z-scores for head circumference, weight and length differed (-0.1 +/- 0.6 > -1.4 +/- 0.6 > -1.9 +/- 0.6; p < 0.0001). Global fat-free mass was less in study infants than the reference infant at the same weight (2062 < 2252 g; p < 0.0001) or gestation (2062 < 2667 g; p < 0.0001). Global fat mass was greater in study infants than the reference infant at the same weight (307 > 198 g, 13 > 8%) or gestation (307 > 273 g; 13 > 9%; p < 0.0001). Changes in central fat mass closely paralleled those in global fat mass (r(2) = 0.76, p < 0.0001).

Reduced linear growth and a reduced fat-free mass suggest that dietary protein needs were not met before discharge. A reduced fat-free mass coupled with an increased global and central fat mass echoes concerns about the development of insulin resistance and metabolic syndrome X in these high-risk infants.