The impact of gestational age and fetal growth on the maternal-fetal glucose concentration difference

Objective: To test whether the human fetus accommodates to the increasing glucose requirements of late pregnancy with an increased maternal-fetal glucose concentration gradient and whether there are differences in pregnancies with fetal growth restriction (FGR) according to clinical severity. Methods: Umbilical venous glucose concentration was measured in 77 normal pregnancies (appropriate for gestational age [AGA]) and 42 pregnancies complicated by FGR at the time of fetal blood sampling. In 40 AGA and in all FGR cases, a maternal ''arterialized'' blood sample was collected simultaneously. Growth-restricted fetuses were subdivided into three groups according to fetal heart rate (FHR) recordings and Doppler measurements of the umbilical artery pulsatility index (PI): group 1 (normal FHR and PI; 12 cases), group 2 (normal FHR, abnormal PI; 17 cases) and group 3 (abnormal FHR and PI; 13 cases). Results: In normal pregnancies with increasing gestational age, there was a significant decrease (P < .001) of umbilical venous glucose concentration and a significant increase of the maternal-fetal glucose concentration difference (P < .001). In addition, there was a significant relation between fetal and maternal glucose concentrations (P < .001). In FGR pregnancies, the maternal-fetal glucose concentration difference was significantly higher in fetuses of groups 2 and 3 compared with normal pregnancies and FGR pregnancies of group 1. Conclusion: In human pregnancy, the fetal glucose concentration is a function of both gestational age and the maternal glucose concentration. In FGR pregnancies, as an accommodation of the fetus to a restricted placental size and placental glucose transport capacity, the maternal-fetal glucose concentration difference is increased, and this increase is a function of the clinical severity.