de Costa 2005 Review
This is a historical review of studies that looked at risk of rupture after a classical cesarean.
Certainly the literature suggests that some classical scars might be more prone to rupture than others. However the risk of rupture of a single well-healed classical Caesarean section scar during a subsequent TOS (Trial of Scar) cannot be determined from any of the studies cited above. It does appear that where there has been no postpartum febrile morbidity and where the placenta in both the current and Caesarean section pregnancies has not been sited under the incision, the risk of rupture for a woman attempting vaginal birth after a single classical Caesarean section might be not much greater than that associated with TOS following one lower segment Caesarean section, and might be similar to that for TOS after two lower segment Caesarean sections, now an acceptable practice. It might also be that in many cases, the scar of a prior classical Caesarean section has already shown its strength by reaching the point of spontaneous labour intact.
Landon et al 2004
This study is the most recent study that includes any information about the risk of rupture for classical, inverted T and J incisions.
Two uterine ruptures were recorded in 105 women (1.9 percent) with a prior classical, inverted T, or J incision who either presented in advanced labor or refused a repeated cesarean delivery.
Lin et al 2003
The original purpose of this study was "to determine the risk of uterine rupture in patients induced with oxytocin or misoprostol after 1 or more previous cesarean sections."
No uterine ruptures occurred in patients with classical or low vertical scars.
Shipp et al 1999
This study compared the risk of rupture between TOLs after low transverse incisions and low vertical incisions.
Conclusion: Gravidas with a prior low vertical uterine incision are not at increased risk for uterine rupture during a trial of labor compared with women with a prior low transverse uterine incision.
Sciscione et al 2008
The objective of this study was to determine if women with a history of a previous preterm cesarean delivery experienced an increased risk of subsequent uterine rupture compared with women who had a previous nonclassic term cesarean delivery.
Conclusion: Women who have had a previous preterm cesarean delivery are at a minimally increased risk for uterine rupture in a subsequent pregnancy when compared with women who have had previous term cesarean delivery.
Patterson et al 2002
The objective of this study was to estimate the maternal and perinatal morbidity associated with cesarean delivery involving the upper uterine segment compared with that of low transverse cesarean delivery.
Conclusion: Classic cesarean section has a higher maternal and perinatal morbidity than inverted T cesarean and much higher than low transverse cesarean. There is no increased maternal or perinatal morbidity if an attempted low transverse incision has to be converted to an inverted "T" incision compared to performing a classic cesarean section.
This is a retrospective study of 157 women who had a pregnancy after a classical c-section. All had repeat c-sections, with .6% rupture and 9% asymptomatic dehiscence and no correlation between scar separation and cervical dilation at time of c-section.
The most recent American College of Obstetricians and Gynecologists practice bulletin on vaginal birth after previous cesarean delivery quotes a 4-9% risk of uterine rupture in the subsequent pregnancy of patients with prior classic cesarean surgery. This figure is correct for combined uterine ruptures and dehiscences but overstates the occurrence of actual uterine rupture in this special patient population.
This is a literature review for both classical and myomectomy scars. The conclusion for classical scars is that scheduled c-section at 36-37 weeks is a reasonable option. For myomectomy scars, they concluded the risks are comparable to low transverse c-section scars. For both sets of scars, authors acknowledge a lack of well-designed studies to formalize conclusions.
Another literature review looking at various risk factors that may contribute to uterine rupture.