Abstract
BACKGROUND: Gestational diabetes mellitus (GDM) is defined as hyperglycemia or glucose intolerance in pregnancy and no history of diagnosed type 1 or type 2 diabetes mellitus. The relationship between elevated glucose without GDM and pregnancy outcomes is not well understood. OBJECTIVES: To examine the relationships between glucose challenge test (GCT) concentrations and GDM with fetal growth and gestational age at birth. METHODS: We conducted a retrospective cohort study using secondary medical record data from Northwestern Memorial Hospital (n = 10,899). The data were from pregnancies where the placenta was sent for pathology. We examined birth weight z-score, gestational age at birth, birth weight to placental weight ratio, small for gestational age, large for gestational age (LGA), and preterm birth. We categorized glucose groups: pass GCT/no GDM (control), fail GCT/no GDM, and GDM. We adjusted linear and log-binomial regression models for maternal age, race, parity, gestational age at birth, and infant sex. RESULTS: Of the placentas sent to pathology, 5% were from pregnancies diagnosed with GDM. Birth weight z-score was marginally higher in the fail GCT/no GDM [adjusted mean difference: 0.14: 95% confidence interval (CI): 0.09, 0.19] and the GDM group (0.19; 95% CI: 0.11, 0.29), compared with the control. The GDM group had a nearly 3-d mean difference in gestational age (adjusted mean difference: ‒2.88; 95% CI: ‒4.00, ‒1.77). Patients in the fail GCT/no GDM group had a higher risk of LGA and preterm birth, by 41% (95% CI: 22%, 63%) and 27% (95% CI: 12%, 44%), respectively. Patients in the GDM group had a 71% (95% CI: 34%, 216%) higher risk of LGA, but preterm birth risk was not significantly different. CONCLUSIONS: GDM was associated with the highest mean birthweight z-score, the shortest mean gestational age, and a higher risk of LGA. Higher glucose concentrations and failed GCT without GDM were associated with a higher risk of preterm birth and LGA.