With the exception of aspartate aminotransferase, all of the analyzed fetal variables were different from the maternal values, and most changed with gestational age. The mechanisms leading to these fetal specificities remain mostly uncertain, but the provision of reference ranges for several blood constituents may be useful in the differential diagnosis of fetal disease.
Diagnostic advances have made it possible to use ultrasonograph to assess placentation and therefore zygosity in utero in the case of monochorionic-monozygotic twins. Foetal behaviour of 15 monozygotic and 15 unlike-sexed dizygotic twin pairs was studied serially with ultrasounds from 10 to 22 weeks gestational age. Each twin, regardless of its zygosity, showed individualised behavioural styles. One twin was found to be 'dominant' in the sense of being more active, but less reactive, possibly due to the fewer stimuli being generated by its co-twin. Monozygotic twins, as opposed to dizygotic twins, showed greater similarities in activity and reactivity levels, but were never behaviourally identical and decreased in likeness with increasing age. Our data suggest that so-called identical twins are very similar, but not behaviourally identical, from very early in pregnancy. The unequally shared intrauterine environment contributes to putting each monozygotic twin on a progressively distinct behavioural path.
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.
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