What is the most serious complication during a vbac?

Uterine rupture. Catastrophic uterine rupture is the most serious complication of attempted vbac (vaginal birth after cesarean section): it can prove lethal for the fetus, the mother or both! If you do not want anymore children, this is too great a risk to take - you may be better off with a prelabor scheduled repeat c-section and bilateral tubal ligation. Talk to your obstetrician!