Prior vaginal delivery, either before or after a cesarean birth, improves the prognosis for a subsequent vaginal delivery with either spontaneous or induced labor (Aviram, 2017; Grinstead, 2004; Hendler, 2004; Mercer, 2008). Prior vaginal delivery also lowers the risk of subsequent uterine rupture and other morbidities (Cahill, 2006; Hochler, 2014; Zelop, 1999).
Women with a nonrecurring indication-for example, breech presentation-have the highest VBAC rate of nearly 90 percent (Wing, 1999). Those with a prior cesarean delivery for fetal compromise have an approximately 80-percent VBAC rate, and for those done for labor arrest, VBAC rates approximate 60 percent (Bujold, 2001; Peaceman, 2006). Prior second-stage cesarean delivery can be associated with second-stage uterine rupture in a subsequent pregnancy Gastrow, 2013).
Most studies show that increasing fetal size is inversely related to VBAC rates. he risk for uterine rupture is less robustly linked. Zelop and associates (2001) studied outcomes of almost 2750 women undergoing TOAC, and the rate of uterine rupture increased-albeit not signiicantly-with rising fetal weight. he rate was 1.0 percent for fetal weight <4000 g, 1.6 percent for >4000 g, and 2.4 percent for >4250 g. Similarly, Jastrow and colleagues (201 Ob) in a retrospective report of 2586 women with a prior low-transverse uterine incision, observed an elevated risk for a failed trial of labor, uterine rupture, shoulder dystocia, and perineal laceration associated with rising birthweights. Conversely, Baron and coworkers (2013) did not ind higher uterine rupture rates with birthweights >4000 g. With a preterm fetus, women who attempt a TOLAC have higher VBAC rates and lower rupture rates (Durnwald, 2006; Quinones, 2005).
Data supporting external cephalic version (ECV) for breech presentation are limited and are derived from small studies (Burgos, 2014; Weill, 2017). From thes;, ECV success and adverse event rates appear comparable to women without prior cesarean. The American College of Obstetricians and Gynecologists (2016) acknowledges this lack of robust data. At Parkland Hospital, we do not attempt ECV in those with a prior cesarean delivery.
Twin pregnancy does not appear to increase the risk of uterine rupture. Ford and associates (2006) analyzed 1850 women with twins and reported a 45-percent successful VBAC rate and a rupture rate of 0.9 percent. Similar studies by Cahill (2005) and Varner (2007) and their colleagues reported rupture rates of 0.7 to 1.1 percent and VBAC rates of 75 to 85 percent. According to the American College of Obstetricians and Gynecologists (2017a), women with twins and a prior low-transverse hysterotomy can safely undergo TO LAC.
Multiple studies have reported an inverse relationship between prep regnancy body mass index (BMI) and VBAC rates. Hibbard and coworkers (2006) reported the following rates: 85 percent with a normal BMI, 78 percent with a BMI between 25 and 30, 70 percent with a BMI between 30 and 40, and 61 percent with a BMI �40. Similar findings were reported by Juhasz and associates (2005).