INTRODUCTION: There has been a dramatic increase in the prevalence of obesity in the past 2 decades almost in all over the world. The purpose of this study was to investigate the effect of body mass index (BMI) increase on obstetric outcomes. MATERIAL-METHODS: Women with singleton pregnancies and deliveries at the obstetric department in Baskent University between May 2004 and August 2005 were included in the study. BMI was calculated prepregnancy and at delivery and the relationships between prepregnancy BMI, delivery BMI and gestational weeks, preterm rupture of membranes (PROM), preterm labor, stages of labor, meconium staining, type of labor, birth weights, birth sexes, postoperative complications were compared. RESULTS: This study included 317 women; 76.2% of women were in normal, 2.4% of them was in obese group prepregnancy. There were no relationships between gestational weeks, type of labor, meconium staining, preterm labor, duration of labor stages, birth weights, postpartum complications, birth sexes, PROM and both initial and delivery body mass indexes statistically (P>0.05). DISCUSSION: Although our results did not support the adverse effects of advanced weight gain, dietary counseling should be offered to the pregnancies.