Objectives: To establish a reference range of insulinlike growth factor 1 (IGF-1) values in normal fetuses and to assess whether intrauterine growth retardation is associated with increased or decreased IGF-1 levels.
Methods: Retrospective analysis of blood samples collected from 64 fetuses who underwent blood sampling at 18-38 weeks' gestation was performed: 40 fetuses, who were considered controls, were appropriately grown for gestational age and were found unaffected by the condition for which they were tested; the remainder (n = 24) underwent fetal blood sampling to assess fetal karyotype and acid-base balance following ultrasonic diagnosis of intrauterine growth retardation. (In this group, 8 survived, and 16 died during the perinatal period). IGF-1 was measured using a radioimmunoassay after acid-ethanol extraction in order to avoid interference by the binding proteins. All samples from controls and growth-retarded fetuses were measured using the same batch, and the intra-assay coefficient of variation of the test ranged from 4.1 to 6.1%.
Results: In control fetuses, IGF-1 serum levels increased linearly with gestational age. In growth-retarded fetuses, IGF-1 levels were not significantly different from the reference range (median Z-score -0.3; range -4.4 to 291) and did not correlate with fetal size, hematocrit, and acid-base balance values. There was a significant difference in IGF-1 and pH values when the fetuses were divided into two groups based on the perinatal outcome: those who survived had values of IGF-1 mostly within the normal range, whereas the fetuses who died in utero or postnatally had significantly decreased pH and elevated IGF-1 values (median Z-score 2.1; 95% confidence interval 0.4-13.9; p = 0.04).
Conclusions: This study confirms previous observations that IGF-1 levels parallel the increase in fetal size which occurs with advancing gestation. Increased levels of IGF-1 may indicate a terminal process in the fetal adaptation to placental failure.