Objective. To investigate the metabolic phenotype and pregnancy outcomes of gestational impaired glucose tolerance (IGT) defined by isolated hyperglycemia during an oral glucose tolerance test (OGTT). Design. Retrospective cohort study. Setting. University referral hospital. Population. A total of 4,789 women were screened for gestational diabetes mellitus (GDM) between 1996 and 2008 with a glucose challenge test (GCT), followed by a 2-hour 75-g OGTT if the GCT result was abnormal; in addition, measurement of plasma insulin concentration during the OGTT was implemented from 2004. Methods. The insulin sensitivity (ISOGTT) and β-cell function (insulinogenic index/homeostasis model assessment for insulin resistance) were calculated for 283 women who underwent a diagnostic OGTT between 2004 and 2008. Perinatal complications were examined in 4,789 women who were screened for GDM between 1996 and 2008. Main outcome measures. Comparison of outcomes among women stratified by glucose tolerance status using the GCT and OGTT profiles. Results. Insulin sensitivity and β-cell function significantly decreased from normal OGTT to 2-hour IGT (single hyperglycemia at 2 hours) to 1-hour IGT (single hyperglycemia at 1 hour) to GDM, with significant differences between normal OGTT and 1-hour IGT or GDM. The occurrence of large-for-gestational age (LGA) neonates was significantly increased in women with GDM or 1-hour IGT (adjusted odds ratio: 2.15, 2.22; 95% confidence interval 1.23-3.75 and 1.04-4.35, respectively) compared to those with normal GCT or normal diagnostic OGTT results. Conclusions. Like GDM, isolated 1-hour hyperglycemia on the OGTT is associated with β-cell dysfunction and an increased risk for LGA neonates.
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