Maternal nutritional status during pregnancy will affect the outcomes for the mother and the newborn. Maternal diet was assessed in 150 pregnant women during the first trimester of pregnancy by a 168-item food frequency questionnaire. Dietary patterns were explored by Factor analysis, and association of patterns with maternal and neonatal outcomes such as gestational diabetes mellitus (GDM), anemia and anthropometric indices were determined by analysis of variance and linear regression analysis. Three major dietary patterns were identified: 1) High Carbohydrate-Lower Fat (mean age, 27.67 ± 6.1; n = 34), 2) High Carbohydrate-Higher Fat (27.70 ± 4.1; n = 55), and 3) High Fiber (29.27 ± 5.8; n = 61). A significant difference was observed between maternal dietary patterns (p < 0.01) for GDM, while it was not significant for anemia. Also, the number of preterm and low birth weight (LBM) infants as well as mean weight, height and head circumference of the infants did not differ significantly between patterns, but there was a significant difference between the maternal dietary patterns about the number of macrosomic babies, which was higher in the second (n = 9) and third (n = 9) dietary patterns (p < 0.01). After adjusting for mothers' age, disease history, disease status, and energy intake, High Carbohydrate-Lower Fat dietary pattern was more associated with GDM than crude model (p = 0.01 vs. p = 0.02). The present study indicated a significant relationship between maternal dietary patterns before pregnancy and GDM and fetal macrosomia.