CESAREAN DELIVERY IN RELATION TO BIRTH-WEIGHT AND GESTATIONAL GLUCOSE-TOLERANCE - PATHOPHYSIOLOGY OR PRACTICE STYLE

Objectives.-To examine the relationship between birth weight and mode of delivery among women with untreated borderline gestational diabetes mellitus (GDM), treated overt GDM, and normoglycemia. Design.-Prospec tive cohort study. Setting.-Three Toronto, Ontario, teaching hospitals . Patients.-A total of 3778 volunteers aged 24 years or older. Interve ntions.-Subjects underwent a 3-hour, 100-g oral glucose tolerance test at 28 weeks' gestation, regardless of screening test results. Usual c are was provided to 143 women who met the National Diabetes Data Group criteria for GDM, Physicians were blinded to glucose test results for all others, including 115 untreated women with borderline GDM by the broader criteria of Carpenter and Coustan. Main Outcome Measures.-Crud e and adjusted rates of cesarean delivery and neonatal macrosomia (bir th weight >4000 g). Results.-Compared with normoglycemic controls, the untreated borderline GDM group had increased rates of macrosomia (28. 7% vs 13.7%, P<.001) and cesarean delivery (29.6% vs 20.2%, P=.02). Ce sarean delivery in this subgroup was associated with macrosomia (45.5% vs 23.5%, P=.03). Usual care of known GDM normalized birth weights, b ut the cesarean delivery rate was about 33% whether macrosomia was pre sent or absent. A clearly increased risk of cesarean delivery among tr eated patients compared with normoglycemic controls persisted after ad justment for multiple maternal risk factors (adjusted odds ratio, 2.1; 95% confidence interval, 1.3 to 3.6). Conclusions.-Infant macrosomia was a mediating factor in high cesarean delivery rates for women with untreated borderline GDM, While detection and treatment of GDM normali zed birth weights, rates of cesarean delivery remained inexplicably hi gh. Recognition of GDM may lead to a lower threshold for surgical deli very that mitigates the potential benefits of treatment.