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During a normal vaginal delivery, the muscle cells propagate electrical signals throughout the uterine wall, resulting in uterine contractions. However, uncoordinated uterine activity may disturb the uterine contractions pattern and negatively impact fetal and maternal health. Some of the abnormalities identified by the specialists are excessively short resting intervals and tachysystole. This work aims to investigate the influence of abnormal uterine activity in terms of maximum principal stress distribution and collagen fibers stretch in the uterine tissue during vaginal delivery with (i) excessively short resting intervals without changing the contraction time, and (ii) tachysystole (contraction and reduced resting times). These patterns are compared with a normal uterine contraction pattern. To achieve our aims, a biomechanical model was developed, including finite element models of the uterus and the fetus, and an electro-chemo-mechanical constitutive model. Generally, the excessively short resting intervals exhibit higher average maximum principal stresses during the contraction and resting stages, lower average fibers stretch values in the longitudinal direction and higher stretch in the circumferential direction. On the other hand, the tachysystole exhibit generally lower stress values during the uterine contraction and higher stress values during the resting stages, higher stretch in the longitudinal direction, and lower stretch in the circumferential direction., (Copyright © 2022 Elsevier Ltd. All rights reserved.)