Background: Macrosomia is defined as birthâweight over 4,000 g irrespective of gestational age and affects 3â15% of all pregnancies. Aim The present study aimed to determine the relationship between mother’s characteristics and macrosomic births and also compare macrosomic and normal newborns regarding the maternal and offspring complications of diabetes during pregnancy. Subjects and Methods: In this case control study, among the 420 consecutive births occurring in public and private hospitals of Shiraz, Iran from October 2006 to March 2007, the data of 32 macrosomic and 128 normal newborns were analyzed using tâtest and chi square in bivariate and logistic regression in multivariate model. Results: The mean (SD) of neonate weight, height, and head size was 3323.4 (709), 48.95 (3.2), and 34.9 (1.8), respectively. Regression analysis showed that gestational diabetes (Odds Ratio (OR): 11.9, Confidence Interval (CI): 4.6â30.3), preeclampsia in the pregnancy period due to diabetes (OR: 3.81, CI: 1.1â13.2), and macrosomic birth history (OR: 3.3, CI: 1.04â10.4) were the main predictors of macrosomia. Moreover, macrosomia increased neonate hypoglycemia (OR: 4.7, CI: 1.4â15.8) and section delivery (OR: 4.1, CI: 1.27â13.1). Conclusion: Gestational diabetes, preeclampsia due to diabetes, and history of macrosomic birth were the main predictors of macrosomia. Moreover, macrosomia increased some delivery complications for both mothers and newborns.