ABSTRACT Objectives: To evaluate the impact of body mass index (BMI) on the timing of labor in relation to the due date of delivery. Patients & Methods: 553 women were evaluated for baseline BMI and classified according to WHO classification. At the time of delivery, BMI was reevaluated and excess BMI gain was determined. Time of delivery in relation to the due date of delivery and the incidence of preterm delivery (PTD) and postdate delivery (PDD) were determined. The relation between time of delivery and at-booking BMI was studied and Kaplan-Meier regression analysis was used to determine the cumulative risk of PTD and PDD at various values of BMI. Results: 35 parturient (6.33%) had PTD with mean gestational age (GA) of 239.8±8.65 days and 20 parturient had PDD at GA of 296.5±1.55 days. Eighteen under and average weights parturient had PTD, while 17 overweight-to-obese II parturient had PTD. PDD was prevalent among overweight-to-obese II parturient. There was a significant correlation between at-booking BMI and incidence of PTD and PDD and Kaplan-Meier regression analysis showed a progressive increase of PTD risk with increased at -booking BMI and risk was 40% for women with BMI of 35 kg/m2 and 80% for women with BMI >35 kg/m2 . Also, the risk of PDD was 100% in women with a BMI of >35 but