Transabdominal versus Transvaginal 2D Ultrasound in Assessment of Lower Uterine Segment Thickness in Females with Previous Cesarean Section: A Comparative Study

Abstract

Summary U ltrasonography has a major role in assisting the obstetrician to evaluate the pregnant uterus. To date its primary focus has beenon the fetus and its development. Paradoxically the organ that houses the fetus during the approximate nine months from conception to birth has received relatively little critical attention and knowledge of the uterine echo features remained scanty. Vaginal birth after previous cesarean section (VBAC) is still controversial. This may be due to the risk of uterine rupture. The rate of uterine rupture varies according to the type and location of the cesarean incision. Because the fetal and maternal consequences of uterine rupture can be serious and life threatening, the proper selection of patients would be an important prerequisite. 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. It is generally considered that, among carefully selected patients who have full participation in decision making, most women with one previous transverse lower segment cesarean delivery are suitable candidates for VBAC and should be offered a trial of labor. Studies have shown that the risk of uterine rupture in the presence of defective scar is related directly to the thickness of the lower uterine segment. 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. Hystrography, hysteroscopy, saline contrast saline sonohystrography and magnetic resonance imaging have all been tried with a variable degree of success. With the availability of ultrasonography, the assessment of the lower uterine segment has become possible. Transabdominal ultrasonography was used to diagnose defects in the scarred uterus by many authors. Others have evaluated the lower uterine segment to detect the presence of scar tissue and its type. Several studies have provedthe value of ultrasonography in this context. Transvaginal sonography has been implicated to predict uterine dehiscence by measuring lower uterine segment thickness prior to the onset of labor. Other studies have implicated transvaginal sonography since the late second trimester. In the present study the main aim of work was to compare between TAS &TVS to find which method of them gives more accurate measurement for lower uterine segment thickness at term by referring the measurement obtained by each of them to the actual measurement taken intraoperative, and finding which method has the best agreement with the actual thickness. The study was conducted at Ain Shams Maternity Hospital and included 144 patients all of them were planned for elective C.S., the patients underwent both TAS examination on partially full bladder and TVS examination on empty bladder to measure L.U.S. thickness from the muscularis and mucosa of the bladder on the outer side to the chorioamniotic membrane inside, with the myometrium in between prior to C.S., the actual thickness of the lower uterine segment was measured intraoperative after delivery of the fetus as the thickness of the LUS was measured by the surgeon using a sterile micrometer. In the whole study casesthe agreement between TVS and actual measures was found to be better than the agreement between TAS and actual measures, although the agreement between both sonographic tools and acual measures was not clinically important. So it may be interpreted that the two methods could be used interchangeably. However, further studies with larger numbers of subjects and blinded observers are needed to validate the degree of LUS thinning with regard to the risk of subsequent uterine rupture.