Abstract. IGF-1 and IGF-2 were measured by specific radioimmunoassay after acid-ethanol extraction of plasma obtained by foetoscopy from 20 normal foetuses aged 15–23 weeks. IGF-1 and IGF-2 levels were 36 ± 11 and 162 ± 55 ng/ml, respectively. In comparison, levels in cord blood were 84 ± 58 and 264 ± 176 ng/ml, respectively, and in adult plasma were 410 ± 106 and 818 ± 272 ng/ml. Both IGF-1 and IGF-2 were in the normal foetal range in a further three foetuses with anencephaly and two foetuses with spina bifida. No sex difference was observed. IGF-1 was positively correlated with foetal body weight (P <0.001), placenta weight (P <0.02) and with body length measured crown-rump (P<0.01) or crown-heel (P < 0.02). No correlation between IGF-2 and body weight, length, placenta weight or gestational age was found. Both IGF-1 and IGF-2 are present in the human foetal circulation earlier in gestation than has previously been demonstrated, the levels being low throughout this period of gestation in comparison with adult plasma.

Abstract. Growth-promoting activity measured as [3H] thymidine incorporation into lectin-activated lymphocytes was determined simultaneously with radioimmunoassayable IGF I and IGF II in cord and capillary blood collected from human neonates 30 min and 24 h after birth. All the parameters studied in cord blood were lower than in normal adults. During the early postnatal period, IGF I decreased and IGF II remained unchanged, but thymidine activity increased above the normal adult level. The differences between the values found in cord blood and in capillary blood collected within the first ½ h after birth agree with a production of growth factors by the infant. All these growth factors may play a role in foetal growth, as suggested by their correlation with birth weight. Finally, factors other than IGFs contributing to thymidine activity may play a role in neonatal growth since they are higher in newborns than in adults.