Objective: To compare labor pattern by body mass index (BMI) in nulliparous women and that may help optimize labor management and ultimately impact the cesarean delivery rate.Study Design: Six hundred (600) pregnant nulliparous women during labor with a singleton term cephalic gestation were assigned in one of the following 3 groups based on their body mass index (BMI) and each group contained 200 women. Repeated-measures analysis constructed average labor curves by BMI categories for those that reached 10cm. The median duration of labor by each centimeter of cervical dilation was computed for normal range group, underweight and obese women and used as a measurement of labor progression.Results: For nulliparas, Labor progressed more slowly with increasing admission BMI. These effects were significant for the active phase of labor (i.e. 4 to 10 cm cervical dilatation) and overall were more pronounced for nulliparas as BMI increases. The mean traverse times to progress from 4 cm to 10 cm was (4.09) hours for BMI < 18.5 kg/m2 compared to (5.36) hours for BMI 18.5-29.9 kg/m2 and (6.08) hours for BMI ≥ 30.0 kg/m2. The mean rate of cervical dilatation was (1.53 cm/hr) for BMI < 18.5 kg/m2 compared to (1.23 cm/hr) for BMI 18.5-29.9 kg/m2 and (1.08 cm/hr) for BMI ≥ 30.0 kg/m2.Conclusion: Labor proceeds more slowly as BMI increases suggesting that labor management be tailored to allow for these differences.