Most of the anatomical changes related to the body of pregnant women occur between the second and third trimesters of pregnancy. The purposes of the study were to quantify the lower limb kinetics of gait and draw a comparison between women in the second and third trimesters of pregnancy, and a nonpregnant group. Subjects and methods: A three-dimensional (3D) kinetic analysis of gait was performed in 24 pregnant and 12 nonpregnant women. Results: Between trimesters of pregnancy, a decrease in the third peak of vertical ground reaction force (GRF) in the third trimester was observed. Most of the changes found between pregnant and nonpregnant women were in the sagittal plane for hip, knee and ankle moments, which report a decrease in mechanical load of the lower limb. In frontal plane a significant decrease in ankle joint moment was found, and in the transverse plane a significant increase in hip moment was found. Joints power decreases for hip and ankle power in sagittal and frontal plane, and increases for hip power in transverse plane. The function of propulsion and mobilization appears to be related to the different changes that occur between the right leg and left. Conclusion: These results suggest that adaptations regarding muscle participation occur first (second trimester), followed by adaptations in muscle power (third trimester). Understanding the biomechanical adaptations during pregnancy may provide more information about mechanical loads, which subsequently will be helpful for prescribing exercise and rehabilitation programs, as well as for the prevention of musculoskeletal injuries.