Thickness of the lower uterine segment: its influence in the management of patients with previous cesarean sections.
Dr. Mohammad Fiaz, M,B;B,S (Pb), MCPS, FCPS 1
Dr Sareena Rasheed, M,B;B,S (Pb) 2
Dr. Hamid Majeed, M,B;B,S (Pb) 3
Dr. Syed Amir Gilani, M,B;B,S (Pb), PhD 4
1-3 Department of Radiology, Services Hospital Lahore, Pakistan.
4 Afro-Asian Institute of Medical Sciences Lahore, Pakistan.
Objective: To determine how ultrasound measurement of the lower uterine segment affects the decision about delivery for patients with previous cesarean sections (CS) and what are the consequences on cesarean section rates and uterine rupture or dehiscence.
Design: Prospective open study. Patients: 150 patients: all women with a previous CS who gave birth in our department during 2001 and 2002 to an infant with a gestational age of at least 36 weeks
Discussion: The aim of this study is to evaluate accuracy of transvaginal sonographic examination of the lower uterine segment in pregnant women with previous cesarean section. METHODS: 150 pregnant women between 37 and 40 weeks of gestation, with previous cesarean section underwent transvaginal ultrasonography. Wall thickness of the lower uterine segment & the length of cervix were measured.
The mean thickness of the lower uterine segment is 3.82 mm +/- 0.99 mm. The transvaginal sonographic examination provides a sensitivity and a specificity respectively of 100 and 75%, for a thickness cut-off of 3.5 mm, and a positive and negative predictive values of 60.7% and 100% respectively. The transvaginal sonographic evaluation of the lower uterine segment improves therefore the obstetrical decision-making regarding the trial of labor in women with previous cesarean section. A prospective randomized study was conducted to measure the serial thickness of the lower uterine segment (LUS) by transvaginal ultrasonography in a study group of 150 women having a history of previous cesarean section (C/S). In the study group, more than 2 mm of thickness of the LUS was considered as good healing and less than 2 mm of thickness as poor healing. After serial sonographic examination, the women with good healing were given trial for labor unless an obstetrical indication for C/S existed. The appearance of the LUS during surgery was compared with antenatal ultrasonographic assessment by direct inspection. 110 (79%) of 150 women with a well healed scar had trial labor with the result that 46% had a successful vaginal birth without any uterine rupture or dehiscence. 30 women with poor healing all had elective C/S. 10 women with a 2 mm LUS thickness were individually categorized for delivery mode. Two of those women delivered vaginally. Two mm or less as a criterion for poor healing had the sensitivity and specificity of 86.7% and 100% respectively. The positive predictive value was 100% and the negative predictive value was 86.7%. Ultrasonographic evaluation is effective in predicting the quality of a uterine scar and in differentiating the risk group of probable uterine rupture from the non risk group. Transvaginal ultrasonography, with its higher frequency and proximity to the pelvic structures has offered us a powerful tool for observing the uterine scar of a previous Cesarean section. We have examined 150 previous Cesarean section scars by transvaginal ultrasonography. Thinning, ballooning and wedge defect were noted. The others were outward or inward protrusions, hematoma formation and inward retraction. An evaluation of the previous section scar, preferably by high resolution transvaginal ultrasonography is highly recommended in considering a trial of labor after previous Cesarean deliveries.
What is a uterine scar rupture?
A complete uterine rupture is a tear through the thickness of the uterine wall at the site of a prior cesarean incision. It is a potentially life threatening condition for both the mother and/or the baby and requires immediate surgical intervention. However, uterine ruptures have also been known to occur in some women who have never had a cesarean. This type of rupture can be caused by weak uterine muscles after several pregnancies, excessive use of labor inducing agents, prior surgical procedure on the uterus, or mid-pelvic use of forceps.
How often does a cesarean scar rupture occur?
For women who had a prior cesarean birth the rupture can occur at the site of the previous uterine scar. Dozens of studies report that for women who have had one prior cesarean birth with a low-horizontal incision, the risk of uterine rupture is about 1% or less. A woman who has had more than one cesarean with a low horizontal incision may have a slightly higher risk of rupture.
What are the symptoms of a uterine rupture?
A uterine rupture cannot be accurately predicted or diagnosed before it actually occurs. It can occur suddenly during labor or delivery. A few studies have suggested that measuring the thickness of the scar by ultrasound or following closely the pattern of contractions in labor may be useful in anticipating and therefore preventing a scar rupture. However, there is not enough information to prove that these methods should be widely adopted.
Results: Uterine dehiscence was found in 9 cases or 4.7%. There were no cases of the uterine rupture. The thickness of the lower uterine segment among the gravidas with dehiscence was significantly less in than those without dehiscence (p< 0.01). The cut-off value for the thickness of the lower uterine segment was 1.6 mm. The sensitivity was 77.8%; specificity 88.6%; positive predictive value 25.9%; negative predictive value 98.7%.
Conclusion: Measurement of the lower uterine segment is useful in predicting the absence of dehiscence among gravidas with previous cesarean section. If the thickness of the lower uterine segment is more than 1.6 mm, the possibility of dehiscence during the subsequent trials of labor is very small. Ultrasound measurement of the lower uterine segment can increase the safe use of trial of labor, because it provides an additional element for assessing the risk of uterine rupture.