|Year : 2015 | Volume
| Issue : 4 | Page : 873-878
Evaluation of lower segment cesarean section scar by sonography
Mohamed S Gad1, Mehany M Abd El Sttar2, Alaa M Abd El Gayed2, Noha F Mahmoud Msc 2
1 Department of Obstetrics & Gynecology, Faculty of Medicine, Al Azhar University, Shibin Elkom, Egypt
2 Department of Obstetrics & Gynecology, Faculty of Medicine, Menoufia University, Menoufia, Egypt
|Date of Submission||13-Oct-2014|
|Date of Acceptance||16-Oct-2014|
|Date of Web Publication||12-Jan-2016|
Noha F Mahmoud
Department of Obstetrics and Gynecology, Faculty of Medicine, Menoufia University, Elmadrasa Elebtdaie Elgadeda Street, Met Om Saleh, Berket Elsabie, Menoufia Governorate, 32651
Source of Support: None, Conflict of Interest: None
This study aimed to correlate lower uterine segment (LUS) thickness measured by both transvaginal (TVS) and transabdominal ultrasonography (TAS) after completion of 36 weeks of pregnancy with that measured manually using a caliper at the time of cesarean delivery and to determine minimum LUS thickness indicative of its integrity in women who have undergone a previous cesarean section.
Ultrasound is used to evaluate the LUS, especially if there is a previous scar, and it is more beneficial to predict the possibility of the occurrence of any complications during labor either by repeated cesarean section or by vaginal delivery.
Patients and methods
Pregnant women admitted to our university hospital at 36-40 weeks' gestation planning for elective cesarean delivery were included in this study. The patients were subdivided into two groups. Group I (study group) included 50 pregnant patients, ±36-40 weeks, with a history of one previous lower segment cesarean section. Group II (control group) included 50 pregnant patients, ±36-40 weeks, with no history of a previous cesarean section. This group was subdivided into two subgroups: IIA included 25 patients in whom elective cesarean section delivery was planned during the period of study because of obstetric indications and IIB included 25 patients with low-risk pregnancies who had vaginal delivery. All patients were examined by both TAS and TVS to evaluate the thickness of the LUS and the thickness was remeasured using a vernier caliper intraoperatively among those who delivered by an elective cesarean section.
Evaluation of the LUS by TVS and TAS and comparison of the results of both with the results obtained by actual measurement intraoperatively indicated that TVS was more reliable and accurate.
Evaluation of LUS scar by TVS is superior compared with TAS.
Keywords: lower uterine segment, previous cesarean section scar, ultrasound
|How to cite this article:|
Gad MS, Abd El Sttar MM, Abd El Gayed AM, Mahmoud NF. Evaluation of lower segment cesarean section scar by sonography. Menoufia Med J 2015;28:873-8
|How to cite this URL:|
Gad MS, Abd El Sttar MM, Abd El Gayed AM, Mahmoud NF. Evaluation of lower segment cesarean section scar by sonography. Menoufia Med J [serial online] 2015 [cited 2020 Feb 17];28:873-8. Available from: http://www.mmj.eg.net/text.asp?2015/28/4/873/173606
| Introduction|| |
To better assess the risk of uterine rupture, some authors have proposed sonographic measurements of lower uterine segment (LUS) thickness near term, assuming that there is an inverse correlation between LUS thickness and the risk of a uterine scar defect. Therefore, this assessment for the management of women with previous cesarean section may increase safety during labor by selecting women with the lowest risk of uterine rupture  .
Transvaginal ultrasound (TVS) examination is a highly accurate method for the detection of cesarean scar defects, for example, in association with abnormal bleeding or thinning of residual myometrium, which may increase the risk of uterine rupture  .
The frequency of LUS scar dehiscence is reported to be similar to the uterine rupture during labor in women with unscarred uterus. Yet, significant numbers of women with previous cesarean births end up having repeat cesarean deliveries. In parous women, previous cesarean section has been found to be the most common indication for the integrity of the scarred LUS during labor and appears to be one of the reasons for a high repeat cesarean rate  .
| Patients and methods|| |
This study recruited 100 pregnant women admitted to our university hospital at 36-40 weeks' gestation planning for an elective cesarean delivery. He local ethical committee at Menoufia University Hospital approved the study protocol, and an informed consent was obtained from all participants before commencing the study. The patients were subdivided into two groups.
- Group I (study group) included 50 pregnant patients, ±36-40 weeks, with a history of one previous lower segment cesarean section.
- Group II (control group) included 50 pregnant patients, ±36-40 weeks, with no history of a previous cesarean section.
- IIA included 25 patients in whom elective cesarean section delivery was planned during the period of study because of obstetric indications.
- IIB included 25 patients with low-risk pregnancies who had vaginal delivery.
This study was carried out to compare the accuracy of TVS versus transabdominal ultrasound (TAS) to assess the thickness of the LUS in pregnant women with a previous cesarean section at term and its correlation with the actual thickness during cesarean delivery.
Nature of the study: This was a prospective comparative observational clinical study.
All the women participating in this study were provided with an explanation about its content, value, and expected complications.
After obtaining informed written consent, all the women included were subjected to the following:
- Full assessment of history, with a special focus on the following:
- Menstrual history, with a focus on the date of the last menstrual period.
- History of previous pregnancy to verify the criteria for inclusion or exclusion.
- Thorough examination including the following:
- General examination: for exclusion of presence of any medical disorders.
- Local obstetric examination:
- Fundal level to correlate with gestational age known by history.
- Umbilical grip to verify inclusion and exclusion criteria.
- Scar tenderness and shape in women who had undergone a previous cesarean section.
- Investigations were performed including the following:
- Basic routine antenatal investigations of pregnant women including blood group, Rhesus factor, complete blood count, blood sugar, and urine analysis.
- Abdominal ultrasound was performed for a complete obstetric assessment within a week before delivery to confirm gestational age, fetal lie and presentation, and placental position, and also to evaluate the LUS thickness. The LUS was visualized in the sagittal section in the mid line and lateral plane. The measurement was obtained with the cursors at the urinary bladder wall-myometrium interface and the myometrium chorioamniotic membrane-amniotic fluid interface. Three layers can be identified by ultrasonography in a well-developed LUS in a midline section of sagittal view in a partially filled bladder. They are as follows from inside outwards:
- Chorioamniotic membrane with decidualized endometrium.
A middle layer of myometrium.
- Uterovesical peritoneal reflection juxtaposed to musculosa and mucosa of the bladder.
- TVS: The thickness of the LUS was measured after emptying the bladder to bring the pelvic organs into the focal zone of the transvaginal transducer. The bladder was identified in the longitudinal plane of the cervical canal. With ultrasonography, the LUS appears as a two-layered structure that consists, from the urinary bladder inward, of the echogenic visceral-parietal reflection, including the musculosa and mucosa of the urinary bladder (the outer layer), and the relatively hypoechoic myometrium layer. The vaginal probe was inserted into the posterior fornix with the patient supine, the knees gently flexed, and the hips elevated slightly on a pillow to allow free movement of the operator. With gentle rotation and angulation of the transducer, both sagittal and coronal images could be obtained.
Measurements were performed using mind ray version 2200 (made in China) and were performed by the same sonographer on both TAS and TVS; the results were not disclosed to the team that would perform the cesarean delivery.
- At the time of surgery, in women who had elective cesarean (not in labor), the LUS was identified as the part of the uterus below the loose reflection of the vesicouterine serosa. After delivery of the neonate, the thickness of the LUS was measured by the surgeon using a sterile metal ruler (vernier caliper) in the following manner: two Green-Armytage 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 Green-Armytage forceps to demarcate the inner surface of the LUS. Vernier caliper was placed on the lower flap of the incision at a right angle to the surface of the grasping forceps and the measurement was obtained.
In women who would not deliver within a week, ultrasound evaluation was repeated to replace the earlier observation.
Then, all measurements were compared. The differences in the observations between the two groups were assessed and analyzed.
| Results|| |
The results were collected, tabulated, and statistically analyzed using an IBM Corp. Released 2011. IBM SPSS Statistics for Windows, Version 20.0. Armonk, NY: IBM Corp. Two types of statistics were done.
- Descriptive, for example, percentage (%), mean, and SD.
- Mann-Whitney test: It is a nonparametric test of Student's t-test. It is used to collectively indicate the presence of any significant difference between two groups for a not normally distributed quantitative variable.
- One-way analysis of variance (ANOVA) (F test): A one-way ANOVA is a single test used to collectively indicate the presence of any significant difference between several groups for a normally distributed quantitative variable.
- Post-hoc test: It is used after one-way ANOVA (F test) or the Kruskal-Wallis test to show any significant difference between the individual groups.
- χ2 -Test: It is used to compare two groups or more for one qualitative variable in a 2 × 2 contingency table or an RC complex table.
[Table 1] shows that both TAS and TVS were 100% specific for the thickness of LUS; it was found that TVS was more sensitive than TAS in terms of the thickness of LUS, and it was also more accurate, with an accuracy rate of 83%, compared with TAS, with an accuracy rate of 75%.
|Table 1 Validity of both TVS and TAS in all cases in terms of caliper results|
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[Table 2] shows that the mean LUS thickness measured by both abdominal, vaginal ultrasound and caliper in group I is less than that of group IIA, with a statistically significant difference. Also, the mean LUS thickness measured by vaginal ultrasound was closer to the measurement of the caliper than that measured by abdominal ultrasound.
|Table 2 Distribution of the studied groups in the thickness of LUS measured by abdominal, vaginal ultrasound, and caliper|
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[Table 3] shows that the thickness of LUS measured by abdominal ultrasound and vaginal ultrasound between primigravida was significantly higher (mean = 5.66 ± 0.74 and 5.65 ± 0.87), respectively, than in the multigravida group (mean = 3.44 ± 1.48 and 3.34 ± 1.56), respectively (P < 0.001).
|Table 3 Relation between the thickness of LUS measured by abdominal ultrasound and vaginal ultrasound and gravidity|
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| Discussion|| |
The uterus plays an important role during pregnancy and parturition. Sonography has proven to be a useful modality to determine whether abnormalities related to the LUS (such as placenta previa or weak previous cesarean section scar) are present, thus decreasing fetal and maternal mortality and morbidity. Ultrasonographically, the LUS appears as a two-layered structure that consists, from the urinary bladder inward, of the echogenic visceral-parietal reflection, including the musculosa and mucosa of the urinary bladder (the outer layer), and the relatively hypoechoic myometrial layer , .
The main aim of this study was to compare TAS and TVS in measurement of the thickness of the LUS at term to determine which method is the most accurate and more reliable to measure LUS by comparing the measurement obtained by each method separately with the actual thickness obtained intraoperatively.
In the present study, the mean thickness of the LUS measured by TAS in those who had a previous cesarean section was 2.49 ± 0.39 mm, whereas the mean thickness of the LUS measured by TVS was 2.34 ± 0.39 mm in the same group. The mean thickness of LUS measured by TAS in those who never had any cesarean section was 5.19 ± 0.81 mm, whereas the mean thickness of LUS measured by TVS was 5.1 ± 0.930 mm. The two sonographic measurements were compared with the actual measurement during the cesarean section delivery and the mean thickness of the LUS was 2.19 ± 0.39 and 5.11 ± 0.91 mm, respectively; this means that the measurement near the actual obtained from TVS.
This was in agreement with the result of Coleman et al.  , who reported that TVS has been known to produce clearer images of the structures of the female pelvis, with proven benefits over TAS.
In this study, the above results were further confirmed by measuring the thickness of the LUS by vernier caliper during cesarean section and on comparing the thickness of LUS in previous cesarean section cases and controls who had undergone elective cesarean section delivery. This relation was found to be highly statistically significant.
It is therefore obvious that the techniques used to measure the LUS thickness and identify uterine defects have not been consistent among different studies, although some studies seemed to report good results with different measurement techniques .
These findings are in agreement with those obtained by Cheung  , who reported that sonography enables accurate assessment of LUS thickness in women who had undergone previous cesarean section which is significantly smaller (1.8 ± 1.1 mm) than normal thickness of LUS.
Last but not the least, these results were found to be in agreement with the study of Fukuda et al.  , who found that the mean thickness of scarred LUS was at least 0.8 mm less than that of intact LUS, and also in agreement with the study of Michaels et al.  , who found the mean thickness of LUS to be significantly less for the abnormal group compared with the controls.
In terms of the relation between LUS thickness in cases with previous cesarean section measured by TVS and TAS and vernier caliper, it was found that the measurements of caliper were closer to those of TVS than those of TAS. This relation was found to be show a significant difference.
For the LUS thickness in cases without previous cesarean section measured by TVS and TAS and vernier caliper, it was found that the measurements of caliper were closer to those measured by TVS than those measured by TAS. This relation was found to show a significant difference.
Kushtagi et al.  , carried out a study to correlate LUS thickness measured by TAS at term pregnancy with that measured manually using vernier caliper at cesarean delivery and to determine the minimum LUS thickness indicative of its integrity in women who had undergone a previous cesarean section. LUS measurement with the caliper was recorded before fetal head delivery than after delivery as LUS would become thicker after delivery with the release of stretch factor of fetus/amniotic fluid and oxytocin. They found that ultrasonographic measurements were correlated with manual measurements of the lower flap of the LUS. Sonographically determined LUS was thinner among women with a previous cesarean delivery than those with vaginal delivery after ceserian section (VBAC). Directly measured LUS thickness before the delivery of the baby showed smaller differences among them. This difference could be because of the inclusion of the posterior wall of the bladder during ultrasonographic measurements. Some stretch of the lower uterine flap may have reduced the thickness to some extent while measuring it with calipers. They suggested that LUS thickness of at least 3 mm measured by abdominal ultrasonography before delivery at term in women with previous cesarean section is suggestive of stronger LUS, but is not a reliable safeguard for trial of labor  .
One of the primary aims of this study was to determine a cutoff value for scar thickness.
Sonographic LUS measurement is increasingly being recognized as a useful clinical tool in the prediction of uterine rupture. Although data from the present study showed the superiority of TAS over TVS for assessment of LUS thickness, the combination of both parameters for the measurement of LUS thickness, if incorporated into guidelines on the management of women who have undergone a previous cesarean section, could provide valuable information in planning for delivery and counseling women undergoing VBAC by predicting its safety and success. It has the potential to be a useful addition to management protocols for women who have previously delivered by a cesarean section.
Rozenberg and colleagues using transabdominal sonographic examination of the LUS at 36-38 weeks' gestation, included the bladder mucosa and the peritoneal layer in the measurement. With a cutoff value of less than 3.5 mm, the negative predictive value was high (99.3%) for predicting uterine defects, but the positive predictive value was low (11.8%)  .
Gotoh et al.  using TVS, concluded that 74% of women with a LUS of less than 2.0 mm had an incomplete uterine rupture at cesarean delivery.
Thickness of the LUS can be measured either by TAS or by TVS ultrasound examination in the third trimester  .
Hebisch and colleagues showed that TVS provided more accurate information about the condition of the scarred LUS than MRI. The main factors that limit an increased use of TVS for the assessment of LUS thickness are discomfort and difficulty in performing the procedure in women at term  .
The study by Cheung et al. suggests that ultrasonographic surveillance for a defective LUS may be possible, but his study population was small, and the observers were not blinded. These preclude accurate estimates and limit the ability to establish clinically useful relationships  ([Figure 1], [Figure 2], [Figure 3]).
|Figure 1 Distribution of the studied groups in the thickness of lower uterine segment (LUS) measured by abdominal ultrasound.|
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|Figure 2 Distribution of the studied groups in the thickness of lower uterine segment (LUS) measured by vaginal ultrasound.|
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|Figure 3 Distribution of the studied groups in the thickness of lower uterine segment (LUS) measured by caliper.|
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| Conclusion|| |
At the end of this work, it is highly recommended that with the increase of the Cesarean section rates ;is to evaluate the scar before the trial of VBAC. Evaluation of LUS scar by TVS is superior compared with TAS. More studies are needed to validate the cutoff value for LUS scar thickness for inclusion in guidelines for the selection of patients for a safe trial of VBAC.
| Acknowledgements|| |
Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]