Objectives: The purpose of this study was to determine the distribution of values for the 75 gm glucose tolerance test in pregnancy and to define glucose intolerance by the relationship between maternal glucose values and neonatal macrosomia.
Study design: A total 3505 unselected pregnant women were given a 75 gm, 2-hour glucose tolerance test. Diet or insulin therapy was offered only to patients with a fasting plasma glucose level > or = 105 mg/dl or a 2-hour post-glucose-load value > or = 200 mg/dl. Birth weights of live-born singletons delivered from 36 to 42 weeks whose mothers had a fasting plasma glucose level < 105 mg/dl and 2-hour post-glucose-load value < 200 mg/dl were used to calculate relationships between glucose levels and birth weights.
Results: At 24 to 28 weeks' gestation the mean and SD plasma glucose values were fasting 83.6 (8.9) mg/dl, 1 hour 128.4 (32.9) mg/dl, and 2 hour 108.4 (24.8) mg/dl. In a multiple logistic regression model the factors found to be statistically significantly associated with macrosomia were maternal race, parity, prepregnancy body mass index, weight gain, gestational age at testing, fasting plasma glucose level, and 2-hour post-glucose-load value. A positive association was found between maternal glucose values and birth weight percentiles. No clinically meaningful glucose threshold values relative to birth weight or macrosomia were found.
Conclusion: In the absence of a meaningful threshold relationship between glucose tolerance test values and clinical outcome, criteria defining gestational diabetes will probably be established by consensus.