Background: Gestational weight gain and BMI play an important role in the outcome of pregnancy. Weight gain during pregnancy based on maternal pre-pregnancy BMI is determined. In This study was evaluated the relationship between body mass index and weight gain of pregnancy with maternal-fetal outcomes.Methods: In this study were enrolled 476 healthy pregnant women with singleton fetus and were divided based on body mass index and weight gain of pregnancy. Information on maternal age, sociodemographic status, parity, early pregnancy weight, gestational weight gain, maternal height, previous history of preterm delivery, nausea and vomiting were collected by a medical-midwifery questionnaire. Phases of labor (delivery), gestational age, mode of delivery, neonatal characteristics and postpartum bleeding was recorded in the delivery information form. After statistical analysis, the relation between body mass index and weight gain during pregnancy, maternal and neonatal outcomes were determined.Findings: Pregnancy outcomes were better in women with normal weight gain. In women, low weight and low weight gain during pregnancy, were more low birth weight. Also, women with overweight and gestational weight gain were exposed higher rates of cesarean delivery and postpartum hemorrhage. Significant differences was found between maternal body mass index with induction of labor, fetal malposition, mode of delivery, birth weight, nausea, vomiting, and weight gain during pregnancy. Women with adequate weight gain had an appropriate outcome in relation to weight, length, head and chest circumference of newborns and methods of delivery and postpartum hemorrhage.Conclusion: Our findings indicate that women with abnormal body mass index in early pregnancy or inappropriate weight gain during pregnancy should have special care to prevent complications of pregnancy and childbirth and protect the health of mother and child.