Previous studies have shown a positive correlation of cord plasma IGF-I and IGBP-3 levels with birth size and gestational age (GA). Whether the levels during extrauterine growth in VLBW infants are similar to those observed in the intrauterine period is not known. Circulating IGF-I, IGF-II and IGFBP-3 were studied longitudinally in 12 ELBW infants on D1, 8, 15, 29, 43, and 57. BW ranged from 624 to 1247 gm, GA: 23 to 29 wks, head size (HC): 21 to 27 cm at birth. All infants were given parenteral nutrition and were switched to enteral feeding gradually. IGF-I and II were measured by radioimmunoassay after removal of binding proteins with acid ethanol cryoprecipitation. IGFBP-3 was measured by a two-site immunoradiometric method. Results are in theTable.

Table 1
Full size table

Postnatal IGF-I, II, IGFBP-3 levels from D1 were significantly lower than cord levels (p<.05). BW was regained by D15 and IGF-I and IGFBP-3 levels did not increase until after D15 at post conceptual GA of 30-32 wks. Both IGF-I and IGFBP-3 correlated sig. with postnatal age**, weight** and HC*(*p<0.01, **p<0.001). IGF-II level varied widely among infants, and there was no sig. correlation with age and body size.

In conclusion, IGF-I & IGFBP-3 but not IGF-II in VLBW infants during the first 8 wks of life are associated with growth in a pattern similar to that seen in the intrauterine period. Serum levels of IGFS and IGFBP-3 never reached the levels found in cord blood.