What tears exactly during repeat c-section pregnancy?

Bad complication: Uterine rupture in pregnancy is a rare and often catastrophic complication with a high incidence of fetal and maternal morbidity. Several factors are known to increase the risk of uterine rupture, but, even in high-risk subgroups, the overall incidence of uterine rupture is low. It is about (0.07%).

Clarify question.: I am not sure what you mean. If you are referring to uterine rupture, then that is a featred complication seen exclusively in failed trials of labor after cesarean section (0.5-10% depending on prior uterine scar) that could prove life-threatening for both mother and fetus.