LOWER UTERINE SEGMENT THICKNESS MEASUREMENT AND UTERINE SCAR INTEGRITY IN PREGNANT WOMEN WITH PRIOR CESAREAN SECTION USING TWO-DIMENSIONAL TRANSABDOMINAL ULTRASOUND: A PROSPECTIVECONTROLLED STUDY IN SHARM INTERNATIONAL HOSPITAL

LOWER UTERINE SEGMENT THICKNESS MEASUREMENT AND UTERINE SCAR INTEGRITY IN PREGNANT WOMEN WITH PRIOR CESAREAN SECTION USING TWO-DIMENSIONAL TRANSABDOMINAL ULTRASOUND: A PROSPECTIVECONTROLLED STUDY IN SHARM INTERNATIONAL HOSPITAL

By

Taha Mohammad Rashad Amer*and Asmaa Ahmad Mohammad Ali**

*MD. Ain Shams University, Department of Obstetrics and Gynecology, Sharm International Hospital, Sharm El-Sheikh, Egypt, E-mail: tahaamer3000@gmail.com

**MSc., Department of Radiology, Sharm International Hospital, Sharm El-Sheikh, Egypt

ABSTRACT

Background: The number of repeated C.S. is steadily increasing, so the risks are suggested to increase. Measurement of the lower uterine thickness (LUS) close to term is an efficient method for prediction of the scar defect and avoiding uterine rupture.

Objective: To determine the normal range of the LUS thickness in pregnant women without prior C.S. near term pregnancy. To evaluate the relationship between the LUS thickness in pregnant women near term with prior one or more C.S. and the occurrence of uterine rupture or scar dehiscence.

Patients and Methods: One hundred pregnant women close to term (36 weeks of gestation or more) with prior at least one C.S. (selected cases) and another one hundred women with prior one or more vaginal deliveries (control group) were enrolled in this prospective controlled and follow up study in Sharm International Hospital. All the cases were assessed for entire LUS thickness by two dimensional transabdominal ultrasound. The study was carried out during the period from 27/6/2020 to 30/11/2021.The selected cases were followed up for the scar condition during their deliveries by repeated C.S... After collection of the data in Exile sheets, they were tabulated and statistically evaluated and analyzed.

Results: The LUS thickness for the controlled group was found 4.1 ± 1.0 mm. with mode equal 4.0 mm, while for the selected group it was found 3.2± 0.897 mm. with mode equal 3.5 mm. The study had showed that the increased time since last C.S. in years is a significantly independent protective factor for scar dehiscence (P=0.038). The cut-off point for LUS thickness as a predictor for scar dehiscence was found < 3.6mm (p=0.002) with sensitivity 80% and specificity 51% and 95% confidence interval (CI).

Conclusion: Pregnant women with prior C.S. whose LUS thickness was found < 3.6mm had to avoid trial for vaginal delivery (VBAC) and to arrange for delivery at shorter gestational age. Recommendations: are to advise to prolong the time elapsed since the last C.S. as the increased time since last C.S. had been found significantly an independent protective factor for scar dehiscence

Key words: Cesarean section (C.S.), rupture uterus, dehiscent scar, lower uterine segment (LUS), transabdominal sonography (T.A.U/S).

INTRODUCTION

     Cesarean section (C.S.) is the most common and well established obstetrical operation worldwide. The adoption of continuous fetal monitoring in the early 1970s contributed to increase in the C.S. rate, resulting in non-progressive labor and suspected fetal distress to become the most common indications for C.S. (Jo. et al., 2018), also there is an increase in number of C.S. on demand and the repeated C.S. (Ulfat et.al., 2019) reported that there is a significant relationship between the transabdominal sonographic measurement of the entire LUS thickness in pregnant women near term who had previous C.S. and the risk of uterine rupture or scar dehiscence. They also considered the LUS thickness an appropriate predictor of dehiscent scars and shorter gestational age in pregnant women with previous C.S.in subsequent pregnancies. The normal LUS appears as a two-layer structure; a hyperechoic layer representing the bladder wall and a less echogenic layer representing the myometrium (Ulfat et al., 2019). The present study was designed to improve the experience of the staff to detect the optimumtime to perform the repeated C.S. according to LUS thickness measurement by two-dimensional transabdominal ultrasound in the third trimester of pregnancy.

PATIENTS AND METHODS

Study design: one hundred pregnant women close to term (36 weeks of gestation or more) with prior at least one C.S. (selected group) and another one hundred women with prior one or more vaginal deliveries (control group) were enrolled in a prospective controlled follow up study in Sharm International Hospital during the period from 27/6/2020 to 30/11/2021.All the women were assessed for the entire LUS thickness by two-dimensional transabdominal ultrasound by the same Radiologist in Radiology Department of the hospital. The selected group was followed up for the scar condition during their deliveries by repeated C.S.

Inclusion criteria of the selected group included one hundred women having single fetus, at 36 weeks of gestation or more, cephalic presentation, with prior one or more C.S. were enrolled in the study. Another one hundred women having single fetus and has no history of C.S. before were recruited as a control group. The study has been approved by the department of Ethical Committee of the hospital and Informed consent was fulfilled for every woman participated in the study.

Criteria of exclusion were: multiple pregnancies, placenta anterior and low lying, Diabetic women and those having fetus > 4 kg. Also, women with placenta accreta and those with history of rupture uterus were excluded. Women who had history of vertical C.S. and those who refused to share in the study were of course excluded.

Ultrasound evaluation and follow-up: transabdominal ultrasonography was performed in the supine position and the woman having moderately filled bladder using two-dimensional ultrasound with convex transducer of frequency 3-5 MHZ in the Radiology Department of the hospital. The examination was done by the same Radiologist for all women. The entire LUS thickness was measured in sagittal section under magnification to localize the thinnest zone. Measurements were obtained at the bladder wall-myometrium interface. The entire LUS thickness was measured as the distance from the posterior bladder wall interface to the uterine amniotic fluid-wall interface (the entire LUS thickness) (Seliger et al., 2018). The selected women with prior C.S. were followed-up during delivery by repeated C.S. for the scar condition.

Statistical analysis: The data were collected in Exile sheets. The data were tabulated and statistically analyzed by an IBM compatible personal computer with SPSS Statistical Package Version 26. Two types of statistics were used:

A.        Descriptive statistics: mean and standard deviation (SD) and mode for quantitative data.

B.        Analytic statistics:

1.   Students t-test (t): is a test of significance used for comparison of quantitative variables between two groups of normally distributed data, while Mann-Whitney’s test (U) for comparison of quantitative variables between two groups of not normally distributed data.

2.   Kruskal-Wallis test (non-parametric test): was used for comparison between more than two groups not normally distributed having quantitative variables.

3.   Tamhane test: is used for Post Hoc analysis. For Probability of error: P value< 0.05 was considered significant.

4.   Receiver Operator Characteristic (ROC) curves with the Area under the CURVE (AUC): was used to determine the optimal cut-off for LUS thickness as a predictor of scar dehiscence.

5.   Sensitivity is the ability of the test to correctly identify those who have the disease.

6.   Specificity: is the ability of the test to correctly identify those who do not have the disease.

7.   Multivariate Logistic regression model was used to detect predictors of scar dehiscence.

RESULTS

     For the selected group; the age in years was 29.55±5.2 years; most of them were around 30 years. The parity was of mean 2.32 ± 1.27, the mode was 1 and 2 (bimodal). The gestational age in weeks was 37.5 ±1.35 and mode was 38 weeks. The estimated fetal weight in grams was 3142 ± 462.9, with mode of 3500 grams. The time elapsed since last C.S. in years was 4 ± 2.23, with mode 4 years. The lower segment thickness in millimeter (mm) was 3.2 ±0.897and mode 3.5 mm for the selected group (Table 1). As for the control group: the mean age in years was 31.38± 5.6 years, with mode 32 years. The parity was 2.83± 1.34 with mode 2. The gestational age in weeks was 38.28 ± 2.03, with mode 40 weeks. The estimated fetal weight in grams was 3215.5 ± 546.2 with mode 3000 grams. The time elapsed since last delivery in years was 4.5 ± 2.4 and mode 3 and 5 (bimodal). The lower segment thickness in millimeter (mm) for the control group was 4.1 ± 1 and mode 4 mm (Table 1).

Correlation between LUS thickness and multiple variants:

     The study has showed that there was a significant negative relationship between LUS thickness and the risk of uterine scar dehiscence in all the studied groups (pTable 2). As regard to the maternal age in years, we found a significant negative relationship with LUS thickness at age group 20—25 years (p= 0.04 - Table 3). We found a significant positive relationship between the gestational age (G.A.) in weeks and the risk of dehiscence of uterine scar in group 39—40 weeks (p=0.044 - Table4). As regard the parity, we have found positive significant association between the number of deliveries and the risk of dehiscent uterine scar at the group of two deliveries (P=0.036 - Table 5). As for the time elapsed since the last delivery in years, we have found insignificant increase in the risk of scar dehiscence when the time elapsed was < 1 year (P= 0.844) and in group of > 4 years (P = 0.062), but significant increase in the risk was found in the group 1.1—2.0 years (P= 0.006) and in group 3.1—4 years (P = 0.094 -Table 6). As regard the amniotic fluid volume (AFV), there was a significant positive association between LUS thickness and average amniotic fluid volume group (P =0.001) and no case of dehiscent scar was reported with oligohydramnios (Table 7). As regard the estimated fetal weight in grams (EFW), we have found a significant increased risk of scar dehiscence in group 3001—3500 grams (P = 0.014). There was also an insignificant increase in the risk in the group of 3501—4000 grams (P =0.211) and there was no risk in the group of > 4000 grams (Table 8). The study has showed that the increased time elapsed since the last C.S. in years was an independent protective factor for scar dehiscence (P = 0.038, confidence interval (CI) = 0.444—0.978 and Odd ratio = 0.659 (Table 10). The cut-off value for LUS thickness as a predictor of scar dehiscence was found < 3.6 mm. (P= 0.002) with sensitivity 80 % and specificity 51 % and 95 % CI (Table 9).

Table (1):  Comparison of characters of control and selected groups

Table (2): Comparison of lower uterine thickness mean± SD(mm) in the studied groups.

P1 between Dehiscent scar group and Intact scar group. P2 between Dehiscent scar group and control group. P3 between intact scar group and control group.

Table (3):  Association between LUS thickness mean± SD(mm) and maternal age (years) in the different studied groups

P1 between dehiscent scar group andintact scar group. P2 between dehiscent scar group and control group. P3 between intact scar group and control group.

Table (4):  Association between LUS thickness (mm) and G.A. (weeks)in the different studied groups

P1 between dehiscent scar group and intact scar group. P2 between dehiscent scar group and control group. P3 between intact scar group and control group.

Table (5):  Association between LUSthickness (mm) and number of deliveries or C.S. in the different studied groups (Parity)

P1 between dehiscent scar group and Intact scar group. P2 between dehiscent scar group and control group. P3 between intact scar group and control group.

Table (6):  Association between LUSthickness (mm) and thetime elapsed science last delivery or CS (years) in the different studied groups

P1 between Dehiscent scar group and Intact scar group. P2 between Dehiscent scar group and control group. P3 between intact scar group and control group.

Table (7):  Association between lower LUSthickness (mm) and amniotic fluid volume (AFV) in the different studied groups

P1 between dehiscent scar group and intact scar group. P2 between dehiscent scar group and control group. P3 between intact scar group and control group.

Table (8):  Association between LUSthickness (mm) and theestimated fetal weight (EFW) (grams) in the different studied groups

P1 between dehiscent scar group and intact scar group. P2 between dehiscent scar group and control group. P3 between intact scar group and control group.

Table (9):Receiver Operator Characteristic (ROC) curve for LUS thickness as a predictor of scar dehiscence

Table (10) showed that the increased time since the last cesarean section (years) is an independent protective factor for scar dehiscence (Odds ratio=0.659, CI= 0.444-0.978).

Table (10): Multivariate Logistic regression for predictors of scar dehiscence

CI= Confidence interval

DISCUSSION

     Most of the studies had used for measurement of LUS thickness transabdominal ultrasound (TA U/S) alone, transvaginal ultrasound (TV U/S) alone or both together. If TV U/S is not available or could not be applied, TA U/S with magnification could be used (Abdel Baset et al., 2010). LUS muscular thickness assessment by TV U/S was found more reliable than the entire LUS thickness by TA U/S approach. Nonetheless, one should consider that the association between thin LUS muscular thickness measurement obtained by TV U/S and the risk of uterine rupture had only been suggested; as all patients evaluated by study in whom LUS was assessed by TV U/S approach and underwent C.S., only uterine dehiscence was observed (Nicol et al., 2010). As our candidates were all Bedwen women; they were unhappy and mostly refused TV U/S approach and only accept TA U/S approach. We evaluated the entire LUS thickness of our candidate by TA U/S approach respecting their preferences. We have to remember also that the actual association between thin LUS measurement and uterine rupture had been assessed only using TA U/S approach (Nicol et al., 2010). Several studies had evaluated the use of ultrasonography in the prediction of uterine rupture, but only few had evaluated the reliability of the method. Lack of reliability in a test may be due to different readings of the same measurement when it is made by the same observer a second time or by a second observer. Unsuitable tests may put patients at risk and entails a waste of resources. In the present study the LUS thickness measurements of all the recruited women were done by the same Radiologist in Radiology Department of the hospital to attain the optimal reliability of the test.

     The current study had showed that LUS thickness measured in millimeter is highly significant thinner in women delivered by C.S. than that in women delivered by normal vaginal delivery. This result was consistent with French study that found that the thinness of LUS was highly correlated with the dehiscent uterine scar and preterm labor (Ginsberg et al., 2013). In Iraq, (Samar and Kadem, 2013) reported that LUS assessment was a simple test that can be used to predict the uterine scar defect, but their study had revealed no reliable cut-off value in this regard. The present study had showed that the LUS thickness measurement in pregnant women with prior C.S. could be used as a predictor of scar dehiscence with a cut-off value < 3.6 mm. with sensitivity 80 % and specificity 51 % and 95 % Confidence Interval. This result was consistent with that of others who reported that the LUS thinning in pregnant women with previous C.S. could be used to predict shorter gestational age and delivery complications with a cut-off value of 3.5—4 mm. with 79 % sensitivity and 84 % specificity (Mohammed et al, 2010 and Naji et al., 2012). The present study has showed that the increased time elapsed since the last C.S. in years is significantly an independent protective factor for scar dehiscence. This result was consistent with other previous studies. (Ulfat et al., 2019) had found that the short duration since last C.S. was significantly correlated with the LUS thinning. It had been reported that the LUS of women delivered by C.S. was healed and become thicker with time (Vervoot et al., 2015). An Indian data stated that women with a short interval between pregnancies had thinner LUS (Balachandran et al., 2014). Also the results of (Basic et al, 2012) supported our finding, as they stated that the duration since last C.S.is correlated positively with the LUS thickness. The important points in our study were that we could find cut-off value for thickness of LUS in pregnant women with prior C.S. below which the risk for scar complication may be suspected which is < 3.6 mm... Also, we could clarify that increasing the time since last C.S. in years is an independent protective factor for scar dehiscence. The limitations of our study were the small number of the recruited women as our hospital is tertiary hospital and most cases were presented or referred as emergency cases, also we could not apply the TV U/S approach for social reasons as our participants are Bedwen women who were unhappy to have this approach.

CONCLUSION AND RECOMMENDATIONS

     The current study had showed that LUS thickness becomes thinner in pregnant women with prior C.S. than in pregnant women who had never had C.S., but only vaginal delivery. The cut-off value of the entire LUS thickness measured by TA U/S in pregnant women with previous C.S.at which we suspect scar problems was found < 3.6 mm. in our study.

Depending on the results of the present study, we could recommend to avoid trial for vaginal delivery after C.S. (VBAC) for women whom LUS thickness is found < 3.6 mm., We also strongly advice to arrange to deliver those women at shorter gestational age to avoid fetal and maternal complications. Another important recommendation is to advice for increasing the time elapsed since last C.S. as it was found that increasing this time is significantly an independent protective factor for scar dehiscence.

ACKNOWLEDGMENTS

     We gratefully thank all the women who had agreed to be enrolled in the study for their cooperation. Deep thanks also are expressed to the clinicians and medical staff at Sharm International Hospital for their logistic and technical support.

     Deep thanks to Doctor Doaa Nasser Mohammed, Assistant Lecturer, Department of Public Health and Community Medicine, Faculty of Medicine, El-Menoufia University, Shebin El-Kom, Egypt for her valuable efforts in statistical analysis of the collected data of the study.

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