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Abstract
Cesarean section is one of the most frequent surgical intervention world wide. Although common place today, this intervention was severely restricted in the past (1). The cesarean section rates increased over 40 years from about 5% to rates well above 20% and kept going up after a short period of decline in the late 80’s to mid 90’s. The cesarean section rate exceeds the recommended rate of 15% in most countries. In Canada and U.S.A. it was 22% in 1999 while in UK it was 19% and in Australia it was 18 - 23% in 1997. In South America it is much higher (Brazil – 27%, Mexico - 24%, Columbia - 33%, Chile - 40%) and these figures would be even higher if only private deliveries are counted (2).
There are a multitude of reasons for this temporal trend including: relative safety of the cesarean section (maternal mortality after cesarean section was estimated to be below 1 per 1000) (3), reduced risk for the fetus (4), avoiding damage to the pelvic floor (5, 6), convenience to the obstetrician in terms of timing and duration of delivery as well as accommodating the concerns and wishes of the patients.
Today, as well as for the last 2 decades in obstetric practice, one of the major topics of debate is decision making in patients with history of previous cesarean birth (7). The old dictum of ’’Once a cesarean=always a cesarean ’’ (8) is no longer applicable because of the awareness of obstetricians about the safety of vaginal birth in a scarred uterus as well as the awareness of greater maternal morbidity and mortality in cesarean birth. The cost of this major operation is also another factor to make the obstetrician think about the trial of vaginal delivery as an alternative of the routine repeat cesarean section(7). It is also to be noted that to reduce the overall rate of cesarean section, it is equally important to reduce the repeat as well as the primary cesarean sections (7).
Attempted vaginal birth after previous cesarean section (VBAC) remains controversial (9¬¬¬¬) ¬¬¬¬¬. Although it has been reported as safe and has contributed to a reduced cesarean delivery rate (10, 11), yet it is associated with a risk of uterine rupture (12). The rate of uterine rupture varies according to the type and location of the cesarean incision (13). Because the fetal and maternal consequences of uterine rupture can be serious and life threatening (14, 15), the proper selection of patients would be an important prerequisite.
It is generally considered that, among carefully selected patients who have full participation in decision making, most women with one previous lower segment transverse cesarean delivery are suitable candidates for VBAC and should be offered a trial of labour (16, 17). Although the efficacy and safety of VBAC have been shown (10, 11), there are no reliable methods to predict the risks of uterine rupture in this group of patients. Studies have shown that the risk of uterine rupture in the presence of defective scar is related directly to the degree of thinning of the lower uterine segment (18, 19). Various imaging modalities have been tried to evaluate the integrity of the scarred uterus and hence to help in selecting patients candidate for a trial of vaginal delivery. Hysterography has been used in the pre-conceptional period but has not proved to be successful (20, 21). Transvaginal ultrasound was used to detect cesarean scars and their defects in the non pregnant state with variable degree of success (22). Saline Contrast SonoHysterography (SCSH) has also been attempted (23).
With the availability of ultrasonography, the assessment of the integrity of the lower uterine scar has become possible even in the gravid uterus (7) ¬. Transabdominal ultrasonography was used to diagnose defects in the scarred uterus by many authors (24). Other authors have worked to evaluate the early puerperal cesarean wound (25). Others have evaluated the lower uterine segment to detect the presence of scar tissue and its type (26). Several studies have proved the value of ultrasonography in this context (7, 9, and 27). Transvaginal sonography has recently been implicated to predict uterine dehiscence by measuring lower uterine segment thickness prior to the onset of labor (28) .Other studies have implicated transvaginal sonography since the late second trimester (19, 29). In Canada, 16% of obstetricians use ultrasound to determine women candidate for VBAC (30). However, the value of applying sonographic scar thickness measurement in management of VBAC remains unclear and needs further study.