title: Cesarean delivery in relation to birth weight and gestational glucose tolerance: pathophysiology or practice style? Toronto Trihospital Gestational Diabetes Investigators.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  Three Toronto, Ontario teaching hospitals.
  
  
  METHODS
  A total of 3778 volunteers aged 24 years or older.
  
  
  METHODS
  Subjects underwent a 3-hour long, 100-g oral glucose tolerance test at 28 weeks' gestation, regardless of screening test results. Usual care was provided to 143 women who met the National Diabetes Data Group criteria for GDM. Physicians were blinded to glucose tolerance test results for all others, including 115 untreated women with borderline GDM by the broader criteria of Carpenter and Coustan.
  
  
  METHODS
  Crude and adjusted rates of cesarean delivery and neonatal macrosomia (birth 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). Cesarean delivery in this subgroup was associated with macrosomia (45.5% vs 23.5%, P=.03). Usual care of known GDM normalized birth weights, but the cesarean delivery rate was about 33% whether macrosomia was present or absent. A clearly increased risk of cesarean delivery among treated patients compared with normoglycemic controls persisted after adjustment 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 normalized birth weights, rates of cesarean delivery remained inexplicably high. Recognition of GDM may lead to a lower threshold for surgical delivery that mitigates the potential benefits of treatment.
authors.affiliation: Department of Medicine, University of Toronto, Ontario, Canada.
authors.forename: C D
authors.initials: CD
authors.lastname: Naylor
authors.forename: M
authors.initials: M
authors.lastname: Sermer
authors.forename: E
authors.initials: E
authors.lastname: Chen
authors.forename: K
authors.initials: K
authors.lastname: Sykora
mesh_terms: D000328:Adult; D001724:Birth Weight; D001786:Blood Glucose; D002585:Cesarean Section / Q000706:statistics & numerical data*; D016640:Diabetes, Gestational / Q000503:physiopathology / Q000628:therapy; D005260:Female; D005320:Fetal Macrosomia; D005951:Glucose Tolerance Test; D006801:Humans; D007231:Infant, Newborn; D016015:Logistic Models; D015999:Multivariate Analysis; D011247:Pregnancy; D011256:Pregnancy Outcome; D011446:Prospective Studies; D012307:Risk Factors
chemical_list: D001786:Blood Glucose