At least three studies report a doubling or tripling of the rupture rate in women with two compared with one prior transverse hysterotomy (.1acones, 2005a; Miller, 1994; Tahseen, 2010). In contrast, analysis of the Network database by Landon and associates (2006) did not conirm this. Instead, they reported an insigniicant diference in the uterine rupture rate in 975 women with multiple prior cesarean deliveries compared with 16,915 women with a single prior operation-0.9 versus 0.7 percent, respectively. As discussed on page 599, other serious maternal morbidity increases along with the number of prior cesarean deliveries (Marshall, 2011).
Imaging of Prior Incision
Sonographic measurement of a prior hysterotomy incision has been used to predict the likelihood of rupture. Large defects in a nonpregnant uterus forecast a greater risk for subsequent rupture (Osser, 201i1). Naji and coworkers (20l3a,b) found that the residual myometrial thickness decreased as pregnancy progressed and that rupture correlated with a thinner scar. In a systematic review, women with a prior low-transverse cesarean incision underwent third-trimester sonographic evaluation (Jastrow, 2010a). Investigators concluded that the thickness of the lower uterine segment was a strong predictor for a uterine scar defect in women with prior cesarean delivery. They deined this segment as the smallest measurement between urine in the maternal bladder and amnionic luid. hat said, they could not ind an ideal threshold value to recommend TOLAC. his same group subsequently recruited 1856 women contemplating vaginal birth after a single low-transverse incision, and they sonographically measured lower uterine segment thickness by between 34 weeks and 39 weeks G as trow, 2016). hey grouped women into three risk categories for uterine rupture during TOLAC based on the measured segment value: high risk <2.0 mm; intermediate risk 2.0-2.4 mm; and low risk �2.5 mm. he TOAC rates were 9,42, and 61 percent in the three categories, respectively. Of the 984 TOLACs, there were no symptomatic uterine ruptures. Overall, data are limited, and this evaluation is currently not part of our routine practice.
Women who have previously sustained a uterine rupture are at greater risk for recurrence. As shown in Table 31-3, those with a previous low-segment rupture have up to a 6-percent recurrence risk, whereas prior upper segment uterine rupture confers a 9-to 32-percent risk (Reyes-Ceja, 1969; Ritchie, 1971). Fox and associates (2014) reported 14 women with prior uterine rupture and 30 women with prior uterine dehiscence. In 60 subsequent pregnancies, they reported no uterine ruptures or severe complications if women were managed in a standardized manner with cesarean delivery prior to labor onset.
Magnetic resonance imaging studies of myometrial healing suggest that complete uterine involution and restoration of anatomy may require at least 6 months (Dicie, 1997). To explore this further, Shipp and coworkers (2001) examined the relationship between interdelivery interval and uterine rupture in 2409 women with one prior cesarean delivery. There were 29 women with a uterine rupture-l.4 percent. Interdelivery intervalsi:;18 months were associated with a threefold greater risk of symptomatic rupture during a subsequent TOLAC compared with intervalsi> 18 months. Similarly, Stamilio and associates (2007) noted a threefold augmented risk of uterine rupture in women with an interpregnancy interval <6 months compared with one �6 months.