Objective: To compare labor patterns by body mass index (BMI). Study Design: 118,978 gravidas with a singleton term cephalic gestation were studied. Repeated-measures analysis constructed mean labor curves by parity and BMI categories for those that reached 10cm. Interval censored regression analysis determined median traverse times adjusting for covariates in vaginal deliveries and intrapartum cesareans. Results: In the labor curves, the time difference to reach 10 cm was 1.2 hours from the lowest to highest BMI category for nulliparas. Multiparas entered active phase by 6 cm, but reaching this point took longer for BMI≥40.0 (3.4hours) compared to BMI<25.0 (2.4hours). Progression by centimeter (P<0.001 for nulliparas) and from 4-10cm (P<0.001 for nulliparas and multiparas) increased as BMI increased. Second stage length with and without an epidural was similar among BMI categories for nulliparas (P>0.05), but decreased as BMI increased for multiparas (P<0.001). Conclusion: Labor proceeds more slowly as BMI increases suggesting that labor management be altered to allow longer time for these differences.