Introduction Excessive body mass index may have adverse effects on the health of women in their perinatal period. Regular physical activity contributes to body mass control. Aim To determine the association of pre-pregnancy and pregnancy BMIs with labor duration in primi- and multiparas. Also, to determine the proportions of pre-pregnancy BMI>25 in women after cesarean sections and vaginal deliveries. Material and Methods Data of 54 women on postpartum day 3 to 5 (29 primiparas: 17 after vaginal and 12 after cesarean deliveries; 25 multiparas: 15 after vaginal and 10 after cesarean deliveries). Demographic data collected from patient’s history included body height, pre-pregnancy and pre-labor body mass, mode of delivery, duration of labor and its second stage, number of deliveries. Pre-pregnancy and pre-labor BMIs were calculated. Results In primiparas there was a moderate positive correlation between pre-pregnancy and pre-labor BMIs and labor duration (r=0.56, p=0.02; r=0.65, p=0.005, respectively). Multiparas did not exhibit a significant correlation between the BMIs and labor duration (p>0.05). Neither of the subgroups showed a significant correlation between pre-pregnancy and pre-labor BMIs and duration of second stage of labor (p>0.05). Among women after vaginal deliveries 15.6% had pre-pregnancy BMI>25; the respective proportion was 22.7% in women after cesarean sections. Conclusions Primiparas with greater pre-pregnancy and pre-labor BMIs were more likely to have longer labor. The proportion of pre-pregnancy BMI>25 was higher for cesarean compared to vaginal deliveries. Physical activity should be promoted in women planning pregnancy to help control BMI.