الفهرس 
Physiology of uterine contractionOnly 14 pages are availabe for public view
 |  | from | 173 |  |  |
| | | from | 173 | | |
Abstract
Ultrasonography has a major role in assisting the obstetrician to evaluate the pregnant uterus. To date its primary focus has been on 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 (Laing, 1991). Vaginal birth after previous caesarean 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 caesarean 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. After years of slowly moving in the direction of establishing VBAC as the norm, prominent obstetricians and the American college of obstetricians and Gynecologists (ACOG) did in about the mid 1990s and began promoting elective repeat caesarean. As a result, the VBAC rates, which had steadily risen since 1980, fell from a peak of 28 percent in 1996 to 21 percent in 2000, a decline of 7 percent. 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 proved the 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 correlation with the actual thickness. The study was conducted at Menofiya Univeristy Hospital and included 100 patients, 75% of them were planned for elective C.S.,25
of them found to have unscarred uteri,50 found to have previous one C.S., the remaining 25were delivered vaginally., 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 before delivery of the fetus as the thickness of the LUS was measured by the surgeon using a sterile metal ruler up to the nearest millimeters. In all the study cases the correlation of the mean thickness of lower uterine segment obtained by TVS was higher than that obtained by TAS, This is also true for patients with unscarred uteri, and previous one C.S., when calculations done for each of them in separate. Therefore, further studies with larger numbers of subjects and blinded observers are needed to correlate the degree of LUS thinning with regard to the risk of subsequent uterine rupture.