Objective :To compare birth weight and cesarean section rates with high gestational weight gain and normal weight gain in nulliparous pregnant women with a normal prepregnant body mass index. Design : A retrospective study. Setting : Thammasat University Hospital. Methods : A study was conducted comparing 330 nulliparous pregnant women with normal prepregnant body mass index who delivered a singleton live birth at Thammasat University Hospital. High gestational weight gain was defined as gestational weight gain greater than 16 kg. The incidence of cesarean rate, neonatal birth weight, selected labor and neonatal outcomes were assessed for the two groups. Statistical analysis was carried out with independent unpaired T-test for continuous variables and Chi-square test analysis for frequency data. Results : No significant differences were found in cesarean section rates between the high weight gain group and the recommended weight gain group (31/196 ; 15.8 % and 23/134; 17.2 % respectively ) .However, the average neonatal birth weight in the high weight gain group was significantly greater than the recommended group ( 3186.3 + 394.1 g and 3062.1 + 358.7 g respectively , p = 0.003). The length of labor and neonatal outcomes were comparable between two groups . Conclusion : High gestational weight gain in pregnant women with a normal prepregnant body mass index was not associated with an increase in the cesarean delivery rate, but it did influence neonatal birth weight. To reduce the risks associated with delivery and their complications, an optimal gestational weight gain for Thai women should be proposed and more studies about gestational weight gain should be performed