['To evaluate whether there is increased maternal or neonatal morbidity in connection with impaired glucose tolerance (IGT) during pregnancy when the condition is not treated.', 'During the study period of 1997-2001, in a defined geographical area in Sweden, the diagnostic criteria for gestational diabetes mellitus (GDM) were limited to the criteria for diabetes. Prospectively, 213 women who were identified with IGT during pregnancy were undiagnosed and untreated. Data on maternal and fetal outcome was collected from records. For each case subject, four control subjects were taken from the same delivery department.', 'The proportion of women who underwent cesarean section was significantly higher in the case subjects than in the control subjects and was independently associated with IGT. The adjusted odds ratio (OR) was 1.9 (95% CI 1.2-2.9). The proportion of infants who were large for gestational age (LGA), defined as birth weight >2 SDs greater than the mean for gestation and sex, was independently significantly associated with untreated IGT during pregnancy (OR 7.3, 95% CI 4.1-12.7). Admission to a neonatal intensive care unit (NICU) for 2 days or longer was more common (adjusted OR 2.0, 95% CI 1.1-3.8). However, 71.3% of the children in the IGT group and 87.3% of the control subjects had no neonatal complications.'] Is maternal and fetal outcomes if gestational impaired glucose tolerance treated?