Objective: To compare pregnancy outcome in a homogeneous group of women with glucose intolerance with that of women without this disorder.

Methods: This was a retrospective cohort study of all women with singleton cephalic-presenting pregnancies delivered at University of Texas Southwestern Medical Center during the period January 1, 1991, through December 31, 1995. During this period, women were screened selectively for glucose intolerance and National Diabetes Data Group thresholds were used to diagnose gestational diabetes. Women with class A1 gestational diabetes were compared with nondiabetic women within the cohort. Effects of confounding variables were analyzed using multiple logistic regression and a matched-control comparison. Controls were matched according to ethnicity, maternal age, maternal weight, and parity.

Results: A total of 61,209 nondiabetic women with singleton cephalic pregnancies were delivered during the study period, and 874 were diagnosed with class A1 gestational diabetes. Women with class A1 gestational diabetes were significantly older, heavier, of greater parity, and more often of Hispanic ethnicity. Hypertension (17 versus 12%), cesarean delivery (30 versus 17%), and shoulder dystocia (3 versus 1%) were significantly increased (all P < .001) in these women compared with the general obstetric population. Infants born to women with class A1 gestational diabetes were significantly larger (mean birth weight 3581 +/- 616 versus 3290 +/- 546 g, P < .001), and this accounted for the increased incidence of dystocia. The attributable risk for large for gestational age (LGA) infants due to class A1 gestational diabetes was 12%.

Conclusion: The main consequence of class A1 gestational diabetes is excessive fetal size leading to increased risk of difficult labor and delivery. We estimate that approximately one of eight women with class A1 gestational diabetes mellitus delivers an LGA infant attributable to glucose intolerance.