OBJECTIVE Women with gestational diabetes mellitus (GDM) show reduced insulin sensitivity and markedly elevated glucose excursions. After delivery, GDM mostly reverts to normal glucose tolerance (NGT), although leaving an increased risk of type 2 diabetes. Because gastrointestinal function changes during pregnancy causing vomiting, constipation, or reduced motility, we thought that gut glucose absorption in GDM or pregnancy might be altered to affect circulating glucose excursions. METHODS By undergoing 180-min oral glucose tolerance tests (OGTTs), pregnant women with GDM (GDMpreg; n=15, BMI=32±2 kg/m2, aged 33±1 years) were compared with NGT women (NGTpreg; n=7, BMI=28±1 kg/m2, aged 34±2 years), matching for major anthropometric characteristics (each P>0.2). After delivery (6-7 months later), both groups were studied the same way. We computed and mathematically modeled gut glucose absorption from insulin-mediated glucose disappearance and endogenous glucose production (EGP). Whole-body insulin sensitivity was calculated using the Clamp-like Index. RESULTS GDMpreg showed 16-25% higher plasma glucose concentrations (P<0.04) during the final 2 h of OGTT, similar EGP, but lower (P<0.01) insulin sensitivity (2.7±0.2 mg·kg(-1)·min(-1) vs. NGTpreg: 4.5±0.8 mg·kg(-1)·min(-1)). In GDMpreg, gut glucose absorption rates were ≤52% lower from 30 to 120 min (P<0.03 vs. conditions after delivery or NGTpreg). In contrast, glucose absorption rates in NGTpreg were comparable during and after pregnancy. None of the studied women developed diabetes after delivery. CONCLUSIONS In GDMpreg, OGTT gut glucose absorption is markedly lower during hyperglycemia, whereas both glycemia and glucose absorption in NGTpreg are comparable between pregnant and postpartum states. Thus, hyperglycemia in GDM does not seem to result from too rapid or increased glucose absorption.