['To examine the relationship of glucose and insulin levels during the 1-hour gestational diabetes screening test to determine their relation to gestational diabetes mellitus (GDM) and possible resulting pregnancy complications.', 'This is a prospective observational study of the delivery records of 784 patients who obtained third trimester screening for both glucose and insulin levels during routine 1-hour 50 g oral glucose load.', 'Insulin levels were positively correlated with glucose levels (p < 0.001). GDM was diagnosed in 17 patients (2.2%). Mean birth weight was not significantly different with glucose levels < 130 pmol/L, 130-140 pmol/L, or > 140 pmol/L (3,282 g, 3,409 g, and 3,310 g, respectively, p = 0.13), nor were 5-minute Apgar scores (p = 0.66). No difference in mean fetal birth weight was found in insulin ranges < 30 pmol/L, 30-60 pmol/L, and > 60 pmol/L (3,330 g, 3,306 g, and 3,276 g, respectively, p = 0.56). Moreover, no significant differences in 5-minute Apgar scores were observed between those groups (p = 0.05). Women who underwent cesarean section (n = 230) had significantly higher glucose and insulin levels than did those who had vaginal deliveries (n = 554) (p = 0.01 and p = 0.003, respectively).'] Are third trimester insulin levels correlated with fetal macrosomia or delivery complications?