|Year : 2020 | Volume
| Issue : 3 | Page : 326-331
Effect of third trimester formation of lower uterine segment on the thickness of previous cesarean scar measured by transvaginal sonography
Asmaa O Moustafa, Samira Y El-Mallah, Hind S Abd-ElMonem
Department of Obstetrics and Gynecology, Faculty of Medicine (Girls), Al-Azhar University, Cairo, Egypt
|Date of Submission||02-Jan-2020|
|Date of Decision||16-Jan-2020|
|Date of Acceptance||20-Jan-2020|
|Date of Web Publication||2-Oct-2020|
Asmaa O Moustafa
Department of Obstetrics and Gynecology, Faculty of Medicine (Girls), Al-Azhar University, Cairo
Source of Support: None, Conflict of Interest: None
Background Several studies have been conducted using various methods to evaluate the correlation of lower uterine segment (LUS) measurement with the risk of uterine rupture or dehiscence, with relative success.
Patients and methods A cross-sectional study was conducted on 200 patients admitted for cesarean section. The patients were subjected to complete general, obstetric examination, and ultrasound measurement of LUS scar by transabdominal ultrasound (TAS) on partially full bladder and by transvaginal ultrasound (TVS) on empty bladder, and measurement of actual thickness intraoperatively.
Results Uterine dehiscence was found in 24 (12%) cases. At 28 weeks, the mean scar thickness as measured by TAS was 6.796±1.84 mm, with a range of 3.6–11 mm, and by TVS was 4.11±1.29 mm, with a range of 3–10.1 mm, and at 38 weeks, the mean scar thickness as measured by TAS was 6.796±1.84 mm, with a range of 3.6–11 mm, and by TVS it was 2.9±0.9 mm, with a range of 1.3–3.9 mm. However, intraoperatively, it was 4.12±1.25 mm, with a range of 3–9 mm, by TVS. The cutoff value was 2.33 mm, and this yields a sensitivity of 96.2% and a specificity of 90%.
Conclusion The LUS scar thickness measured sonographically is a good predictor of uterine scar dehiscence in pregnant women at term with previous cesarean section. Data from the present study demonstrated the superiority of TVS over TAS for the assessment of LUS scar thickness.
Keywords: lower uterine segment, transabdominal ultrasound, transvaginal ultrasound
|How to cite this article:|
Moustafa AO, El-Mallah SY, Abd-ElMonem HS. Effect of third trimester formation of lower uterine segment on the thickness of previous cesarean scar measured by transvaginal sonography. Sci J Al-Azhar Med Fac Girls 2020;4:326-31
|How to cite this URL:|
Moustafa AO, El-Mallah SY, Abd-ElMonem HS. Effect of third trimester formation of lower uterine segment on the thickness of previous cesarean scar measured by transvaginal sonography. Sci J Al-Azhar Med Fac Girls [serial online] 2020 [cited 2020 Oct 31];4:326-31. Available from: http://www.sjamf.eg.net/text.asp?2020/4/3/326/296924
| Introduction|| |
Cesarean section (CS) was introduced into obstetrics late in the 19th century. The number of women undergoing an elective cesarean delivery has increased worldwide over the past few decades . One of the most common indications for cesarean delivery is a previous cesarean delivery . It is usually indicated when vaginal delivery puts risk to the health and well-being of the mother and/or the fetus , owing to antepartum hemorrhage, dystocia in labor, preeclampsia, malpresentation, fetal distress, preterm infant and very low birth weight, suspected fetal macrosomia, fetal congenital anomalies, and prevention of mother to child transmission of infections of HIV, human papilloma virus, and herpes simplex virus .
CS is associated with a greater risk of complications such as intermenstrual bleeding, chronic pelvic pain and secondary infertility, uterine lacerations, bladder injury, ureteric injury, bowel injury, postpartum endomyometritis, wound infection, urinary tract infections, thromboembolic complications, hospital readmission after delivery, obesity of offspring, adhesions, and cesarean scar ectopic pregnancies .
Wound healing is a complex process, which includes inflammation, angiogenesis, new tissue formation, and tissue remodeling, which finally leads to at least partial reconstruction of the wounded area . Evidence revealed a pivotal role of growth factors, step by step released from the serum of injured blood vessels and by degranulating platelets, neutrophils, monocytes, lymphocytes, fibroblasts, and tissue specific cells .
Diagnosis of CS scar defects can be performed by ultrasonography, hysterosalpingography, and hysteroscopy. Transvaginal unenhanced ultrasound examination can be used for detection of CS defects. High-resolution transvaginal ultrasound (TVS) is a valuable tool for detection of myometrium thinning or scar dehiscence .
Repeated ultrasound during pregnancy is very helpful in assessment of a multitude of factors, including gestational age, amount of liquor, fetal presentation, and estimated fetal weight and excluding congenital anomalies. However, the two most important parameters are the condition of the scar and the placental location and adherence .
Reports have shown that uterine dehiscence is a high-risk condition for uterine rupture and that measurement of the lower uterine segment (LUS) thickness before the onset of labor may have a great clinical significance . The thinning in the LUS is considered to be the result of a stretching in a portion in the LUS caused by the gestation itself. Ultrasound also has been used by clinicians to diagnose uterine rupture before the onset of labor, and recently, researchers have tried to predict which women are at increased risk of uterine rupture, as during pregnancy, the uterine wall gets progressively thinner .
The study aimed to compare the accuracy of TVS versus transabdominal ultrasound (TAS) to measure the LUS scar thickness at CS.
| Patients and methods|| |
This was a cross-sectional study conducted between September 2018 and April 2019 at the Obstetrics and Gynecology Department in Faculty of Medicine, Al-Zahra University Hospital.
The herein trial was performed with the approval of Research Ethics committee at the Faculty of Medicine for Girls, Al-Azhar University. Data access permission has been issued from the Egyptian Forensic Medicine Authority.
The study was done on 200 pregnant patients, who were sure of dates and willing to participate in study (after taking written consent), and they were recruited from ANC clinic at 28 weeks and were followed up at 38 weeks.
Pregnant women without any medical disorders affecting the course of labor, singleton pregnancy, normal ultrasonography findings (fetal structures and placental site), and cephalic vertex presentation were included.
Patients with grossly contracted pelvis, placenta previa, and previous vesico-vaginal fistula repair were excluded.
LUS scar thickness was measured by both two-dimensional TAS on partially full bladder and then TVS on the same setting but after voiding, before the CS. The actual thickness of LUS was measured intraoperatively using a sterile metal ruler after delivery of the neonate and then compared between the results of the measurements.
Examinations were performed using a transabdominal convex array transducer. The examination was performed with a partially full bladder. A clear view of the LUS was obtained in the midsagittal plane in an adequately magnified view. The thickness of the LUS was measured as a single measurement from the mucosa of the bladder on the outer side to the chorioamniotic membrane up to one-tenth of a millimeter.
With an empty bladder, the patient was examined in the dorsal position with flexion of thighs and knees. The transvaginal probe tip was lubricated with coupling gel to avoid air trapping, and introduced to the vagina. CS scar defect was diagnosed in the presence of a hypoechogenic area (a filling defect) within the myometrium of the LUS, at the site of a previous cesarean incision. Once identified, the myometrium defects were evaluated regarding the following parameters: scar width (the length of the widest gap along the cervico isthmic line), scar depth (the vertical distance between the base and the apex of the defect), and thickness of residual myometrium (from the apex of the defect to the uterovesical peritoneum).
Two (Allice) forceps were used to hold the lower flap of the uterine defect about 2 inches apart on either side of the midline. The flat upper end of a grasping forceps was placed on the inner aspect of the LUS between the two Allice forceps to demarcate the inner surface of the LUS. A sterile ruler was placed on the lower flap of the incision at a right angle to the surface of the grasping forceps, and the measurement was taken .
There are three layers that can be identified in the LUS in pregnancy using B-mode two-dimensional TVS, which are the chorioamniotic membrane with the decidualized endometrium; the middle muscular layer; and the uterovesical fold (peritoneal reflection seen as a hyperechoic line juxtaposed with the muscularis and mucosa of the bladder ([Figure 1]).
|Figure 1 Images demonstrating measurement of the entire thickness of the lower uterine segment (LUS) by transabdominal two-dimensional (a) and three-dimensional (c) ultrasound and of the muscular layer of the LUS by transvaginal two-dimensional (b) and three-dimensional (d) ultrasound.|
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TVS was done to assess the LUS thickness. This is defined as the shortest distance between the urinary bladder wall-myometrium interface and the myometrium/chorioamniotic membrane-amniotic fluid interface ([Figure 2]).
|Figure 2 TVS showing the LUS and bladder full. Open arrow indicates the uterine wall; solid arrow indicates the bladder wall. LUS, lower uterine segment; TVS, transvaginal ultrasound.|
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In cases of a previous elective CS, the scar appears halfway between the uterovesical fold and the internal cervical os, whereas following emergency CS, the scar could be well below, or at the level of the os. The aforementioned approach has been tested prospectively and associated with scar-detection rates of ∼92% in anteverted uteri and 66% in retroverted uteri where poor scar visibility seems to be an issue. All cases in this study were elective CS.
Statistical calculations were performed using SPSS, version 21 (SPSS Inc., Chicago, Illinois, USA). The statistical significance of differences in categorical data was determined using the c2 test, and the statistical significance of differences in continuous data using the independent sample t test. P value less than or equal to 0.05 was considered statistically significant.
To determine which measurements best predicted whether a scar defect in the lowest scar was subjectively perceived to be large by the ultrasound examiner, receiver operating characteristics (ROC) curves were drawn separately for women who had undergone one and those who had undergone two CSs. The area under the ROC curve was calculated with its 95% confidence interval. The measurement was considered to have discriminatory potential if the lower limit of the confidence interval for the area under the ROC curve exceeded 0.5. The measurement with the largest area under the ROC curve was considered to be the best predictor of a defect being perceived to be large by the ultrasound examiner. The best cutoff value mathematically was defined as that corresponding to the point situated furthest from the reference line.
| Results|| |
Of the 200 pregnant women with previous CS presented to the Gynecology and Obstetrics Department of Al-Zahra University Hospital for repeated CS, 35 cases did not reach 38 weeks, owing to early CS because of two factors − decrease amniotic fluid or decrease blood supply to fetus ([Table 1]).
|Table 1 Descriptive analyses of age, time since the last cesarean section (year), thickness of lower uterine segment (mm) at 38 weeks, and fetal birth weight (g)|
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[Table 2] reveals that 88% of the cases had intact scar thickness (3–9 mm) and 12% of the cases had uterine dehiscence with scar thickness less than 3 mm, without any case of complete uterine rupture intraoperatively at the time of delivery.
[Table 3] illustrates that most of the studied cases had only one previous section (54%).
[Table 4] shows that on comparing the mean thickness of CS scar by TAS (6.79±1.84 mm) with that obtained by TVS (4.11±1.29 mm) at 28 weeks, there was a statistically significant difference between the two measurements (P<0.001).
|Table 4 Comparison between the transabdominal ultrasound and transvaginal ultrasound scar measurements at 28 weeks in all the studied cases|
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[Table 5] shows that the mean thickness of CS scar by TAS was 6.79±1.84 mm compared with 2.9±3.9 mm obtained by TVS at 38 weeks, and there was a statistically significant difference between the two measurements (P<0.001).
|Table 5 Comparison between the transabdominal ultrasound and transvaginal ultrasound scar measurements at 38 weeks in all the studied cases|
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[Table 6] compares the actual mean thickness (4.12±1.25 mm) with mean thickness by TAS (6.79±1.84 mm), which was considered statistically insignificant (P<0.001).
|Table 6 Comparison between the actual intraoperative measurements and the transabdominal ultrasound in all the studied cases|
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[Table 7] also compares the actual mean thickness (4.12±1.25 mm) with mean thickness by TVS (4.11±1.298 mm), which is considered statistically insignificant (P<0.05). Therefore, TVS was more accurate than TAS when comparing both to intraoperative LUS thickness (4.11, 6.79, and 4.12 mm, respectively).
|Table 7 Comparison between the actual intraoperative measurements of the scar and the transvaginal ultrasound in all the studied cases|
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[Table 8] reveals the relation between the number of CS and scar dehiscence. Among studied cases with three or more CS, there was a higher significant percentage than those with only one CS (66.7 vs. 16.7%, P<0.05).
[Table 9] shows the mean scar thickness as measured by TVS at 28 weeks, which was 4.11±1.29 mm with a range of 3–10.1 mm, and at 38 weeks was 2.9±0.9 mm, with a range of 1.3–3.9 mm (P<0.001).
|Table 9 Comparison between the transvaginal ultrasound scar measurements at 28 weeks versus 38 weeks in the studied cases|
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[Table 10] and [Figure 3] show the ROC curve analysis for predicting the best cutoff value for detection of scar dehiscence, which was 2.33 mm by TVS measurement of the lower CS scar, that is, less than or equal to 2.45 mm was a prediction of scar dehiscence, with a sensitivity of 96.2% and specificity of 90.0%.
|Table 10 Receiver operating characteristics curve for prediction of scar dehiscence using transvaginal ultrasound measurement at third trimester|
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|Figure 3 Receiver operating characteristics curve for prediction of scar dehiscence using TVS measurement at third trimester. TVS, transvaginal ultrasound.|
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| Discussion|| |
Cesarean delivery has been increasingly performed for a variety of clinical indications. Most uterine incisions are made transversely in the lower segment, where fibrous tissue is abundant. This allow the scar to heal more securely .
Repair of the uterine incision may be in a single layer or multiple layers because of differences in myometrium contraction on either side of the incision. The superior edge of the incision typically is thicker than the inferior edge. This discrepancy often contributes to the development of the lower segment defects noted on sonographic examination .
In this study, we described the value of LUS thickness measurement in the prediction of uterine defects during CS in women who had undergone a previous one or more CS.
The mean scar thickness as measured by TVS at 28 weeks was 4.11±1.29 mm, which ranged from 3 to 10.1 mm, and at 38 weeks was 2.9±0.9 mm, which ranged from 1.3 to 3.9 mm. These figures are in agreement with those of Sen et al.  who stated a mean scar thickness in the third trimester of 3.3±1.09 mm. This finding was consistent with the previous data reported in Japan by Fukuda et al.  which revealed the same mean of LUS thickness but are slightly lower than the study by Vincent et al. , which reported a scar thickness in the third trimester of 1.9±1.4 mm.
Hebisch et al.  compared the results of ultrasonography with those of MRI. They demonstrated that vaginal ultrasonography provided more accurate information about the condition of the scarred myometrium of the isthmus than MRI.The study results determined a cutoff value for this scar thickness that can be clinically used with safety. This cutoff value must yield the best sensitivity and specificity in order not to have many CS for really good scars and at the same time not to jeopardize the life of the mother and the fetus in a useless trial of labor. This naturally has its implication on the diagnosis, prognosis, and policy of delivery.
In this study, a ROC curve was constructed using the scar thickness in the third trimester (36–40 w) and then determining the sensitivity and specificity with a range of cut-off value. We found that a best cutoff value will be at 2.33 mm, and this yields a sensitivity of 96.2% and a specificity of 90%. This is consistent with the study by El-Ebrashy et al. , which found that the best cutoff value will be at 3 mm (using TVS), and this yields a sensitivity of 78% and a specificity of 81%. At this cutoff value, the positive predictive value is 80% whereas negative predictive value is 50%, with an accuracy of 76% .
Conclusion and recommendations
The LUS scar thickness measurement is most accurate with TVS in comparison with TAS. Ultrasonography evaluation permits better assessment of the risk of intrapartum complications for patients attempting VBAC, and could allow for safer management of delivery. Moreover, the measurement of LUS scar thickness by ultrasound, if it is used for both inpatients and outpatients, could help decision making regarding the mode of delivery for patients with prior vaginal birth after cesarean section.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]