he risk of uterine rupture in women with a prior vertical incision that did not extend into the fundus is unclear. Martin (1997) and Shipp (1999) and their coworkers reported that these low-vertical uterine incisions did not have an increased risk for rupture compared with low-transverse incisions. The American College of Obstetricians and Gynecologists (2017a) concluded that although evidence is limited, women with a prior vertical incision in the lower uterine segment without fundal extension may be candidates for TOLAC. This is in contrast to prior classical or T -shaped uterine incisions, which are considered by most as contraindications to labor.
Although there are few indications for a primary classical incision, 53 percent of women undergoing cesarean delivery between 24°/7 weeks and 256r weeks have such an incision (Osmundson, 20l3). By 28 weeks' gestation, the risk drops to 35 percent and declines to < 10 percent by 32 weeks. he likelihood of classical uterine incision is also increased by noncephalic presentations. In those instances-for example, preterm breech fetus with an undeveloped lower segment-the "low vertical" incision almost invariably extends into the active segment. Prior preterm cesarean delivery may result in a twofold increased risk for rupture (Sciscione, 2008). This may be in part explained by the greater likelihood with a preterm fetus of upward uterine incision extension. Lannon and coworkers (2015) compared 456 women with a prior periviable cesarean delivery with more than 10,000 women whose prior cesarean delivery occurred at term. hey observed uterine rupture in 1.8 percent in the prior periviable group versus 0.4 percent in the prior term group. Of the uterine ruptures in the periviable group, half were in women whose prior uterine incision was described as low transverse. Harper and associates (2009) did not confirm these findings.
There are also special considerations for women with uterine malformations who have undergone cesarean delivery. Earlier reports suggested that the uterine rupture risk in a subsequent pregnancy was greater than the risk in those with a prior low transverse hysterotomy and normally formed uterus (Ravasia, 1999). But, in a study of 103 women with miillerian duct anomalies, there were no cases of uterine rupture (Erez, 2007).
Given the wide range of risk for uterine rupture associated with the various uterine incision types, it is not surprising that most fellows of the American College of Obstetricians and
Gynecologists consider the type of prior incision to be the most important factor when considering a TOLAC (Coleman, 2005).
As discussed in Chapter 30 (p. 577), the low-transverse hysterotomy incision can be sutured in either one or two layers. A metaanalysis by Roberge and colleagues (2014) compared single-versus double-layer closure and locking versus unlocking suture for uterine closure. They reported that rates for uterine dehiscence or uterine rupture for these closures did not difer signiicantly. Single-layer closure and locked irst layer, however, was associated with a reduced myometrial thickness during subsequent sonographic measurement. In contrast, Bennich and coworkers (2016) reported that a double-layer closure did not increase the residual myometrial thickness when saline contrast sonography was done several months postpartum. At Parkland Hospital, we routinely close the lower-segment incision with one running, locking suture line.
Number of Prior Cesarean Incisions