Uterine Rupture in Labor: Risk Factors, Timing, and Statistics

Question
Hi Dr. Rappaport, Thank you for taking my question.  I'm doing some research on uterine rupture in pregnancy/birth.  I'm having a difficult time finding out WHEN in labor a uterine rupture is most likely to occur-- and what the stats are.  Is it 70% chance of happening in pushing and 30 % prior to even first stage labor?  I've heard of a mom who had a uterine rupture and she hadn't even started labor yet---at 38 weeks.  So I'm curious if you know the stats or how I can search pubmed properly.  Thank you so much.  

Answer
I don't have the statistics at hand. However, uterine rupture is usually seen in patients attempting VBAC or if they are on pitocin stimulation. It is very rare for rupture to start prior to labor or in the first stage in women with no history of a uterine incision. Certainly, there is a 1% risk of rupture in women who have had a previous cesarean section and who go into labor. As long as there is careful monitoring and attention to the fetal heartbeat and the patient, there usually is not problem.