Journal of Womens Health, Issues and Care ISSN: 2325-9795

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Research Article, J Womens Health Issues Care Vol: 4 Issue: 4

Is Transvaginal Sonography Better than Transabdominal Sonography in Estimating the Thickness of Lower Uterine Segment? A Prospective Observational Study

Chanderdeep Sharma*, Mukesh Surya, Anjali Soni, Pawan Kumar Soni, Ashok Verma and Suresh Verma
DR R P G M C Kangra, Tanda, Himachal Pradesh, India
Corresponding author : Chanderdeep Sharma, MD
(OBG), DNB (OBG), Assistant Professor (OBG), DR R P G M C KANGRA at Tanda, Himachal Pradesh, India-176001
Tel: 91-9218925471
E-mail: [email protected]
Received: December 12, 2014 Accepted: June 24, 2015 Published: June 27, 2015
Citation: Sharma C, Surya M, Soni A, Soni PK, Verma A, et al. (2015) Is Transvaginal Sonography Better than Transabdominal Sonography in Estimating the Thickness of Lower Uterine Segment? A Prospective Observational Study. J Womens Health, Issues Care 4:4. doi:10.4172/2325-9795.1000195

Abstract

Is Transvaginal Sonography Better than Transabdominal Sonography in Estimating the Thickness of Lower Uterine Segment? A Prospective Observational Study

 

To compare the trans-abdominal ultrasonography (TAS) with trans-vaginal sonography (TVS) for assessing the thickness of lower uterine segment (LUS) and myometrium (MYO) in pregnant women. Design: A prospective observational study

Keywords:

Keywords

Transvaginal; Transabdominal sonography; Caesarean scar; Lower uterine segment; Myometrial thickness

Introduction

Recent times have seen an alarming rise in the rates of cesarean section (CS) worldwide [1-3]. Majority of pregnant women presenting to obstetricians are with previous CS. Furthermore, previous CS itself is becoming leading indication for CS [1].
The risk of rupture of previous CS scar is 0.2-1.5% [4]. Ultrasound estimation of lower uterine segment (LUS) provides a fairly simple and non-invasive method for prediction of scar dehiscence or rupture [5-8]. The successful outcome of trial of labor in women with previous CS depends on the scar of previous CS, which is directly related to its thickness [5]. Evaluation of thickness of LUS has been found to be a potential factor for predicting scar dehiscence [6]. The risk of scar dehiscence or rupture has been directly related to the thinning of LUS [7]. However, there is limited data available on comparison of measurement of LUS thickness by trans-vaginal or trans-abdominal sonography [8,9].
We performed a PubMed database search for trials comparing transabdominal sonography (TAS) & transvaginal sonography (TVS) for assessment of LUS in pregnant women published in the English literature between 1990 and 2014, using key words “transabdominal”, “transvaginal” “sonography,” “pregnancy,” “lower uterine segment,” and “cesarean scar.” We found only two trials that compared TAS with TVS for assessing thickness of LUS in pregnant women [8,9].
Hence, the present study was planned to determine the correlation between thickness of LUS, as measured by TAS & TVS with actual thickness measured during CS; to help the obstetricians in making evidence based decision for measurement of LUS thickness in pregnant women with previous CS. It may further aid in decision regarding mode of delivery; thereby reducing rates of repeat CS and to prevent catastrophic outcomes like rupture uterus leading to severe fetal & maternal morbidity & mortality.

Materials and Methods

We conducted a prospective observational study for comparing the TAS with TVS for assessment of LUS and myometrial thickness in pregnant women. This study was conducted in the department of Obstetrics & Gynaecology in close collaboration with the Department of Radio-diagnosis of Dr. Rajendra Prasad Government Medical College and Hospital, Tanda Kangra, India, which is a tertiary care teaching hospital providing routine & emergency obstetric care to nearly 10,000 women per annum for both high risk & low risk pregnancies. The recruitment took place from June 2013 to December 2013 after obtaining the approval from the institutional ethics committee. The trial was also registered on the trial registry of India (www.ctri.nic.in vide number CTRI/2013/04/004991).
All women posted for elective CS were approached for enrolment. Women were eligible for inclusion if they had singleton pregnancy between 36 to 41 weeks of period of gestation and were planned for elective CS as per obstetrical indications. Exclusion criteria were active labor, multiple pregnancy, low lying placenta, leiomyoma in LUS of uterus, previous classical cesarean section/hysterotomy, previous uterine surgery other than cesarean section (myomectomy, hysterotomy, polypectomy, lysis of uterine synechia, or hysteroscopic metroplasty).
Written informed consent was obtained from all the participating women. Subsequently, women were divided into three groups. Group 1 consisted of women with no previous CS, group 2; women with previous one CS & Group 3 included women with previous two CS.
All these women underwent ultrasound evaluation of the LUS and myometrium one day prior to the scheduled surgery. All the ultrasonic measurements were done by the same skilled examiner (M.S.). Examinations were performed with a scanner (GE Logic P5, GE Healthcare) consisting of a trans-abdominal convex array transducer with a frequency of 3 MHz and a transvaginal probe with a frequency of 8 MHz. The thickness of the LUS and myometrium was assessed by a sonogram perpendicular to the uterine wall, according to the technique proposed by Jastrow et al. [10] To measure the thickness of LUS, a cursor was positioned at the interface between the urine and the bladder wall and another cursor between the amniotic fluid and the decidua [10]. The myometrial thickness was measured with the cursor at the interface of the bladder wall and the myometrium so that it included only the hypoechogenic layer. Three different values of LUS & myometrium were taken & lowest of these was taken as final value. To optimize the measurement of LUS, the distension of the bladder was done by a standardized procedure according to Bujold et al. [11]. Women were instructed to empty their bladder and then drink 300 millilitres of water one hour before the examination. If during the ultrasound examination uterine contraction was observed, the examination was stopped & resumed after the contraction had subsided. Ultrasound was also done from the lateral aspect of LUS to detect any asymptomatic dehiscence. Any funnelling, ballooning or wedge defect was noted. Age, parity, gestational age, and neonatal birth weight was assessed for all the women.
At the opening of the abdominal wall during CS, surgeon made an objective evaluation of the integrity and thickness of the LUS into four separate grades, as described by Qureshi et al. [12] The LUS was graded as follows: Grade I (LUS was well-developed). Grade II (LUS was thin without visible content), Grade III (LUS was translucent with visible content) and Grade IV (LUS had well-circumscribed defects, either dehiscence or rupture). All the surgeries were performed by one surgeon (C.D) to eliminate inter-observer variation in assessment of LUS. The operating surgeon was blinded to the ultrasonic evaluation of the LUS or myometrium.
LUS was identified as the part of the uterus below the loose reflection of the vesico-uterine serosa. After the delivery of neonate, two Green-Armytage forceps were used to hold the lower flap of the uterine incision about two inches apart on either side of the midline. The flat upper end of a grasping forceps was placed on the inner aspect of the lower uterine segment between the two Green-Armytage forceps to demarcate the inner surface of the LUS. A sterile calliper 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 at three different places one centimetre apart each & lowest value was taken as the thickness of the LUS.
Statistical analysis was performed by SPSS 17 software for Windows, using parametric and non-parametric tests when appropriate. The normality of the distribution was assessed by the Kolmogorov-Smirnov test. Continuous data was analyzed with the t-test, and categorical variables were analysed with the Fisher’s exact test, when appropriate. P<0.05 was considered statistically significant. Correlation between LUS measurement by TAS & TVS with actual thickness of LUS (as observed intra-operatively) was assessed using Spearman rank correlation co-efficient (rs). Further Bland- Altman plot was made for assessing which of the two measurement techniques (TAS or TVS) is better for assessment of LUS thickness and myometrial thickness.

Results

One hundred and seven women were eligible for inclusion in the study. Three women in group 1 & four women in group 2 went into spontaneous labor before elective cesarean section and as per study protocol were excluded from the study. So, there were 50 women in group 1(50%), 40 in group 2 (40%) & 10 in group 3 (10%). As shown in Table 1, there was no significant difference in the parity (abortion or previous vaginal delivery), gestational age, neonatal birth weight or sex of the neonate in either group. However, there was significant difference in the maternal age 25.1 ± 4.0, 27.6 ± 2.8, & 29.4 ± 3.2 years (mean ± SD: P=0.000) and indications for CS (P=0.000) in three groups.
Table 1: Demographic Characteristics of Women.
Out of all pregnant women, (on the basis of intra-operative assessment) 85 women had grade I LUS (fifty in group 1, twenty eight in group 2 and seven in group 3), eleven women had grade II, and two women each had grade III & IV (one each in group 2 & 3 respectively) {p value 0.001}, as shown in Table 2. One woman each in group 2 & group 3 had scar dehiscence (thickness of LUS; 2.5 mm and 2.6 mm respectively) as shown in Table 2. None of the women in the study had uterine scar rupture or funnelling, ballooning or wedge defect in the LUS.
Table 2: Intra-Operative Grading Of LUS As Observed Intra-Operatively In Women.
Table 3 shows the mean thickness of LUS as measured by TAS & TVS in three different groups (TAS group 1, 2 & 3: 4.80 ± 1.08, 3.97 ± 0.83 & 3.93 ± 1.12 mm and TVS group 1, 2 & 3: 4.93 ± 1.16, 4.04 ± 0.79 & 4.15 ± 0.99 respectively) and myometrial thickness as measured by TAS & TVS in three groups was 2.11 ± 0.89, 2.47 ± 0.59 & 3.20 ± 0.57 mm and 2.08 ± 0.79, 2.56 ± 0.62 and 3.33 ± 0.70mm, respectively. The mean thickness of LUS was significantly different in these three groups p value (0.000).
Table 3: Thickness of Lower Uterine Segment (LUS) and Myometrial Thickness in Women as Measured by Trans-Abdominal (TAS LUS) and Trans-Vaginal Sonography (TVS LUS).
Table 4 shows the correlation between measurements of LUS by TAS & TVS with actual intra-operative measurement during CS. Overall both TAS & TVS had equally good correlation (rs 0.843. 0.847 & 0.837 respectively in three groups). On further comparison of TAS with actual measurement of LUS correlation was 0.819, 0.823 & 0.066 respectively and of TVS with actual LUS measurement it was 0.827, 0.814 & 0.541 respectively in three groups. Women with previous two CS (group 3), TVS had superior correlation as compared to TAS (rs=0.541 versus 0.066). On comparison of myometrial thickness measurement between TAS & TVS correlation was 0.796, 0.873 & 0.763 respectively in three groups as shown in Table 4.
Table 4: Association Between Actual Thickness of LUS And Thickness of LUS as Measured by TAS & TVS and Myometrial Thickness as Measured by TAS & TVS.
Figure 1 shows the Bland-Altman plot to compare the two measurement techniques (TAS & TVS) for measurement of LUS in (a) all women in the study (b) group 1 [women with unscarred uterus] (c) group 2[women with previous one CS ] & (d) group 3 [women with previous two CS]. Similarly, Figure 2 shows Bland- Altman plot to compare two measurement techniques (TAS & TVS) for measurement of myometrial thickness in (a) all women in study (b) group 1[women with unscarred uterus] (c) group 2 [previous one CS] & (d) group 3 [women with previous two CS]. As clearly observed in two figures, almost all the measurements lay between two standard deviations of mean, thereby implying that both the techniques are equally good for measuring LUS and myometrial thickness.
Figure 1:a,b,c,d: Bland-Altman Plot (a): To compare two measurement techniques of LUS thickness (TAS & TVS) in all women (b): To compare two measurement techniques (TAS & TVS) for measurement of LUS thickness in group 1 (women with unscarred uterus) (c): To compare two measurement techniques (TAS & TVS) for measurement of LUS thickness in group 2 (women with previous one CS) (d): To compare two measurement techniques (TAS & TVS) for measurement of LUS thickness in group 3 (women with previous two CS).
Figure 2:a,b,c,d: Bland-Altman Plot (a): To compare two measurement techniques (TAS & TVS) for myometrial thickness in all women. (b): To compare two measurement techniques (TAS & TVS) of myometrial thickness in women in group 1 (unscarred uterus). (c): To compare two measurement techniques (TAS & TVS) of myometrial thickness in group 2 (women with previous two CS). (d): To compare two measurement techniques (TAS & TVS) of myometrial thickness in group 3 (women with previous two CS).

Discussion

Main findings
In the present study we observed both TAS & TVS to be equally efficacious in estimating the thickness of LUS and myometrium in pregnant women.
Strengths
Our study followed a well-defined methodology [10-12] for measuring the LUS thickness (intra-operatively along with subjective assessment of LUS) and adequate urinary bladder filling before doing ultrasound examination. Also, a single radiologist performed all the ultrasound scans and a single surgeon (blinded to the results of ultrasound) performed all the surgeries thereby eliminating the interobserver bias.
Limitations
Limitation of our study is less number of women with previous two CS (n=10). Hence our results can not accurately predict the efficacy of TAS with respect to TVS for assessing the thickness of LUS in women with previous two CS. Also due to single observer for intra-operative and sonographic measurements each can lead to intra-observer bias.
Interpretation
All pregnant women with previous CS should be offered a trial of labor [13]. Recently there has been a sharp fall in the number of women opting for trial of labor after CS, due to rare but catastrophic occurrence of scar rupture resulting in severe fetal & maternal; morbidity & mortality [13]. To further complicate the decision making, this event cannot be reliably predicted [14].
Estimation of LUS and myometrial thickness by ultrasound, has a promising potential to predict scar dehiscence or rupture in women with previous CS [4,5,7,15-17]. The actual thickness of LUS and specifically myometrium has been shown to be associated with successful trial of labor in women with previous CS [18-20]. The measurement of LUS before delivery has been studied as a predictive factor for estimating the risk of dehiscence or rupture of uterus in pregnant women [19,20].
Actual thickness of LUS measured intra-operatively, has been compared with TAS in women with previous CS by several investigators [4,5,8,21]. Sen et al. [5] categorized LUS into four grades (grade 1; well-developed LUS & grade 4; scar dehiscence or rupture), Cheung et al. [4] measured LUS as a dichotomous categorical variable, Suzuki et al. [21] observed sub-peritoneal separation in LUS as evidence of dehiscence and Marasinghe et al. [8] directly measured the thickness of LUS with calipers (they observed no dehiscence or rupture of scar). So as to achieve the best possible prediction of scar dehiscence/rupture, we observed both actual LUS thickness with calipers as well as subjective categorization of LUS as done by Sen et al. [5].
Our observation of equal efficacy of TAS & TVS in estimating the thickness of LUS, is contrary to the available literature [8,9]. Till date only two studies on this subject are available. The primary aim of Martin et al. [9] was to evaluate the reliability of two & threedimensional ultrasonographic measurement of LUS in pregnant women by TAS & TVS. They did not measure the exact thickness of LUS intra-operatively. Furthermore, they observed a very small number of women (n=30). Marasinghe et al. [8], even though measured the actual measurement of LUS thickness intra-operatively but the confounding factor of inter-observer variations, both by ultrasonographer and operating surgeons; was not adequately addressed in their trial. None of these two studies measured myometrial thickness, which is an added advantage in our study, as the risk of scar dehiscence has been suspected to be more associated with “myometrial thickness” rather than “the whole thickness of LUS” [10].
No available study in the literature (to the best of our knowledge) has assessed the comparison of myometrial thickness by two techniques of TAS & TVS. In our observation, both these techniques are equally efficacious in assessment of myometrial thickness. This observation may have a wider application in terms of applicability of this knowledge to general population, especially in low resource populations.
Even though TVS examination has potential benefits of better resolution & clear imaging of the female pelvis [22-25] but in the present era of evidence based medicine these observations do not translate into better evaluation of LUS thickness in pregnant women, as shown by our observations.
Hence, our study provides one of the best insights into the dilemma regarding optimal use of ultrasound for estimating the thickness of LUS. Accurate prediction of thickness of LUS in pregnant women (which further has been found to be associated with increased risk of scar dehiscence/rupture) can be of great help in decision making to obstetricians & pregnant women with previous CS, thereby minimizing the unnecessary need of elective CS as well as early decision to avoid labor which might lead to uterine dehiscence/ rupture.

Conclusion

To conclude, our study demonstrates that both TAS & TVS are equally efficacious for estimating the thickness of LUS and myometrium in pregnant women. It can be helpful in the management plan of women with previous CS by aiding obstetricians in better prediction of scar dehiscence or rupture in women with previous CS. However, their accuracy in women with more than one previous CS needs to be further evaluated.

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