Recent studies suggest that gestational diabetes mellitus (GDM) is underdiagnosed. To test this hypothesis, we examined the relationship of perinatal complications to glucose tolerance during the third trimester. Our population consisted of 287 women evaluated at ∼28 wk gestation who had normal fasting (<5.9 mM) and 2-h (<9.2 mM plasma glucose) levels after a 100-g glucose load. Glycosylated hemoglobin and glycosylated plasma protein were also measured. Study subjects were stratified into three groups based on 2-h plasma glucose values: group 1 (n = 59) <5.6 mM, group 2 (n = 112) 5.6–6.0 mM, and group 3 (n = 116) 6.7–9.2 mM. There were statistically significant but low correlations (r < 0.20) between 2-h plasma glucose levels and mother's age, body mass index, infant weights, and Apgar scores. There was a significant increasing trend in the proportion of overweight and obese women from groups 1 to 3 (P < 0.02). There was also a significant trend toward higher birth weights (P = 0.013) and larger proportions of large for gestational age (LGA) babies (P = 0.02) from groups 1 to 3, and women with LGA infants showed higher fasting and 2-h plasma glucose levels than women with non-LGA infants (P = 0.032). However, there was no significant difference in perinatal complications or infant morbidity or mortality between groups. Percentage of glycosylated hemoglobin or glycosylated plasma protein did not differ between groups. In conclusion, mother and infant size are significantly related to 2-h plasma glucose, but we found no increased risk of perinatal complications with increased 2-h plasma glucose if <9.2 mM, suggesting that the current criteria for GDM are adequate for detecting women at risk for complications in our patient population.

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