Abstract
ObjectivesThe placental transfer of nutrients is influenced by maternal metabolic state, placenta function and fetal demands. Human in vivo studies of this interplay are scarce and challenging. We aimed to establish a method to study placental nutrient transfer in humans. Focusing on glucose, we tested a hypothesis that maternal glucose concentrations and uteroplacental arterio-venous difference (reflecting maternal supply) determines the fetal venous-arterial glucose difference (reflecting fetal consumption).MethodsCross-sectional in vivo study of 40 healthy women with uncomplicated term pregnancies undergoing planned caesarean section. Glucose and insulin were measured in plasma from maternal and fetal sides of the placenta, at the incoming (radial artery and umbilical vein) and outgoing vessels (uterine vein and umbilical artery).ResultsThere were significant mean (SD) uteroplacental arterio-venous 0.29 (0.23) mmol/L and fetal venous-arterial 0.38 (0.31) mmol/L glucose differences. The transplacental maternal-fetal glucose gradient was 1.22 (0.42) mmol/L. The maternal arterial glucose concentration was correlated to the fetal venous glucose concentration (r = 0.86, p<0.001), but not to the fetal venous-arterial glucose difference. The uteroplacental arterio-venous glucose difference was neither correlated to the level of glucose in the umbilical vein, nor fetal venous-arterial glucose difference. The maternal-fetal gradient was correlated to fetal venous-arterial glucose difference (r = 0.8, p<0.001) and the glucose concentration in the umbilical artery (r = −0.45, p = 0.004). Glucose and insulin concentrations were correlated in the mother (r = 0.52, p = 0.001), but not significantly in the fetus. We found no significant correlation between maternal and fetal insulin values.ConclusionsWe did not find a relation between indicators of maternal glucose supply and the fetal venous-arterial glucose difference. Our findings indicate that the maternal-fetal glucose gradient is significantly influenced by the fetal venous-arterial difference and not merely dependent on maternal glucose concentration or the arterio-venous difference on the maternal side of the placenta.
Highlights
Fetal development comprises the entire intrauterine process of differentiation, growth and maturation between conception and birth
The maternal arterial glucose concentration was correlated to the fetal venous glucose concentration (r = 0.86, p
The maternal-fetal gradient was correlated to fetal venous-arterial glucose difference (r = 0.8, p
Summary
Fetal development comprises the entire intrauterine process of differentiation, growth and maturation between conception and birth. The net transfer of glucose over the placenta is thought to be influenced by the maternal-fetal glucose concentration gradient, surface area, transporter density and glucose metabolism of the placenta as well as blood flow [9, 12,13,14,15]. The maternal-fetal gradient will increase with lower glucose levels on the fetal side of the placenta. Studies of GLUT transporter densities showed different responses to hyperglycaemia depending on whether the exposure was in vivo or in vitro [15]. This observation probably reflects that in vivo there are multiple factors influencing transporter expression and activity. Glucose and insulin concentrations in maternal and fetal circulations are reported in smaller human studies, of which several were performed during the stress of vaginal delivery [17,18,19,20]
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