Transplacental supply of mannose and inositol in uncomplicated pregnancies using stable isotopes

Abstract

Objective: The aim of this study was to determine relative contributions of transplacental flux vs. fetal production for inositol and mannose in normal term pregnancies. Study Design: Seven term uncomplicated pregnancies undergoing cesarean section were infused with 13C- and 2H-labeled isotopes of glucose, inositol, and mannose until a steady state was achieved. Maternal and fetal concentrations of labeled and unlabeled glucose, mannose, and inositol were measured using gas chromatography/mass spectroscopy. The fetomaternal molar percentage excess ratio was calculated for each glucose, mannose, and inositol. Results: The fetomaternal molar percentage excess ratio of mannose in the fetal artery (Fartery/M) was 0.99 [97.5% confidence interval (CI), 0.91-1.07] and in the fetal vein (Fvein/M), 1.02 (97.5% CI, 0.95-1.10). Both were not significantly different from 1.0, consistent with transplacental supply. Thefetomaternal ratios for glucoseweresimilar tomannose(fetal artery, 0.95;97.5%CI, 0.84-1.15; and fetal vein, 0.96; 97.5% CI, 0.85-1.07). The fetomaternal ratio for inositol was significantly less than 1.0 (fetal artery, 0.08; 97.5% CI, 0.05-0.12; fetal vein, 0.12; 97.5% CI, 0.06-0.18), indicating little transplacental flux and significant fetal production. Conclusion: In normal term pregnancies, fetal mannose and glucose concentrations are dependent upon maternal transplacental supply. Fetal inositol is not dependent upon transplacental supply. Copyright © 2012 by The Endocrine Society.