Effect of intrauterine growth retardation on postnatal changes in body composition of preterm infants.

To find the effect of intrauterine growth retardation on postnatal changes in body composition, we studied nine preterm small for date (SFD) and 9 gestation matched appropriate for gestational age (AGA) infants (mean +/- SD birth weight - SFD : 1431 +/- 16I g, AGA : 1904 +/- 223 g, gestational age - SFD; 237 +/- 9 days, AGA : 236 +/- 7 days). Total body water (TBW) and extracellular water (ECW) were measured at birth, on the day of maximum weight loss and on regaining of birth weight. Body solids were calculated from the difference between TBW and body weight. SFD infants had significantly less postnatal weight loss (64 +/- 19 g) than AGA infants (135 +/- 49 g; P < 0.01) and showed a significant gain in body solids (19 +/- 12 g) during this period which was not seen in AGA infants (-4 +/- 14 g; P < 0.05). The subsequent weight gain occurred at similar rates in SFD (16 +/- 4 g/day) and AGA (18 +/- 6 g/day) infants, but a significantly higher ratio of the weight gain consisted of solids in SFD as compared to AGA infants (P < 0.05). Per unit of body weight, SFD infants had significantly less body solids (213 +/- 12 g/kg) than AGA infants (228 +/- 18 g/kg; P < 0.05) at birth, but by the time birth weight was regained the two groups of infants had similar probody solids (SFD: 248 +/- 7 g/kg, AGA : 255 +/- 12 g/kg). These results suggest that in SFD infants catch-up growth starts early, during the period of apparent weight loss.