Full Lower Uterine Segment Thickness Research Articles

Accuracy of sonographic lower segment thickness and prediction of vaginal birth after caesarean in a resourced-limited setting; Prospective study.

To assess the accuracy of ultrasound measurement of the lower uterine segment (LUS) thickness against findings at laparotomy, and to investigate its correlation with the success rate of vaginal birth after one previous caesarean delivery (CD) in a resource-limited setting. Prospective study. Obstetrics and Gynaecology department in a tertiary hospital in Ghana. Women with one previous CD undergoing either a trial of labour (TOLAC) or elective CD. Myometrial lower uterine segment thickness (mLUS) and full lower uterine segment thickness (fLUS) were measured with transvaginal ultrasound (TVUS). The women were managed according to local protocols with the clinicians blinded to the ultrasound measurements. The LUS was measured intraoperatively for comparison with ultrasound measurements. Lower uterine segment findings at laparotomy, successful vaginal birth. A total of 311 pregnant women with one previous CD were enrolled; 147 women underwent elective CD and 164 women underwent a TOLAC. Of the women that underwent TOLAC, 96 (58.5%) women had a successful vaginal birth. The mLUS was comparable to the intraoperative measurement in the elective CD group with LUS thickness <5 mm (bias of 0.01, 95% CI -0.10 to 0.12 mm) whereas fLUS overestimated LUS <5 mm (bias of 0.93, 95% CI 0.80-1.06 mm). Successful vaginal birth rate correlated with increasing mLUS values (odds ratio 1.30, 95% CI 1.03-1.64). Twelve cases of uterine defect were recorded. LUS measurement ≤2.0 mm was associated with an increased risk of uterine defects with a sensitivity of 91.7% (95% CI 61.5-99.8%) and specificity of 81.8% (95% CI 75.8-86.8%). Accurate TVUS measurement of the LUS is technically feasible in a resource-limited setting. This approach could help in making safer decisions on mode of birth in limited-resource settings.

Intrapartum ultrasound measurement of the lower uterine segment thickness in parturients with previous scar in labor: a cross-sectional study

BackgroundThere is a lack of reliable methods to estimate the risk of uterine rupture or dehiscence during a trial of labor in women with previous cesarean sections. This study aimed to assess the lower uterine segment and myometrial thickness by ultrasonography in women with previous cesarean sections during labor and assess their association with the uterine defect.MethodsA cross-sectional study was conducted on 161 women in the active phase of labor having one previous cesarean section. The study was conducted et al.-Azhar University Hospital, Assiut City, Egypt, from March 2018 to March 2019. Ultrasound measurements of lower uterine segment thickness and myometrial thickness were conducted by vaginal and abdominal ultrasound by two observers. The correlation of both thicknesses with the uterine defect was analyzed.ResultsUterine defects were reported in 42 women (25.9%), uterine rupture in four women (2.5%), and dehiscence in 38 women (23.5%). The uterine defects were not associated with maternal factors (maternal age, gestational age at labor, body mass index, birth weight, interpregnancy, and inter-delivery interval). Receiver operating curve analysis demonstrated that lower uterine segment thickness was linked with uterine defect, with an area under the curve of 60% (95% CI, 51–70%, P = 0.044). Myometrial thickness was also linked to the uterine defect, with an area under the curve of 61% (95% CI, 52–71%, P = 0.025). Full lower uterine segment thickness of 2.3 mm and myometrial thickness of 1.9 mm were the cutoff value with the best combination of sensitivity and specificity for the uterine defect. Lower uterine segment thickness (OR = 0.49, 95%CI 0.24–0.96) and myometrial thickness (OR = 0.44, 95%CI 0.20–0.94) were significantly associated with the uterine defect. Lower uterine segment thickness (OR = 0.41, 95%CI 0.22–0.76) and myometrial thickness (OR = 0.33, 95%CI 0.16–0.66) were also significantly associated with cesarean section delivery.ConclusionA lower uterine segment thickness of 2.3 mm and myometrial thickness of 1.9 mm during the first stage of labor are associated with a high risk of uterine defects during a labor trial. These measurements during labor can have a practical application in deciding the mode of delivery in women with previous cesarean sections and might reduce uterine rupture.

Can ultrasound predict the delivery time of patients with previous cesarean section in the 37th gestational week? A prospective cross-sectional study

Background The aim was to investigate factors that predict when patients with previous cesarean section will undergo cesarean section (CS) using ultrasonography in the 37th gestational week. Material and methods In this prospective cross-sectional study, a total of 166 patients with previous CS who presented to the hospital for routine checks at the 370/7th gestational week were included in the study. Uterine-related, fetus-related, and patient-related factors that affect labor time were analyzed by the same physician at admission, and the patients were then divided into two groups as those having CS at early term (370/7 to 386/7 weeks of gestation) and full-term (390/7 to 406/7 weeks of gestation). Ninety-four patients underwent CS at full-term and 72 patients underwent CS at the early term in the study. Results There was no significant difference for age (years), parity, weight gain, previous cesarean number, cervical length, myometrial thickness, estimated fetal weight, and full lower uterine segment thickness between the groups (p>.05). In the full-term group, 58% had a history of vaginal birth, whereas, in the early-term group, 42% had a history of vaginal birth (p < .05). Vaginal birth history was found to be independently associated with reaching full-term (respectively, OR: 2.876, 95% CI: [1.227–6.738]; p = .015) in all patients. Two different regression models were created to predict different CS times after the 37th week of pregnancy. Weight gain was found to be independently associated with CS time within the first seven days after admission (OR: 1.267, 95% CI: [1.003–1.599]; p = .047). Vaginal birth history and estimated fetal weight were found to be independently associated with CS time in the 8th day and further after admission (OR: 0.244, 95% CI: [0.089–0.675]; p = .007 and OR: 1.002, 95% CI: [1.000–1.003]; p = .047) Conclusion Vaginal birth history can be useful to predict reaching full-term in patients with previous CS. Determination of such risk factors is important in terms of reducing the frequency of emergency cesarean delivery.

Does Lower Uterine Segment Thickness Measurement Improve Birth Planning After Previous Cesarean Section?

Lower uterine segment (LUS) thickness measurement is frequently used to select patients for trial of labor after a previous cesarean section (TOLAC). To date no significant benefit of LUS measurement has ever been proven, and no standard protocol or clear cut-off value exists. The aim of this study was to evaluate the benefit of LUS measurement in a daily routine setting. In this retrospective study, we evaluated 631 pregnancies after previous cesarean section (CS). Ultrasound measurements of myometrial (mLUS) and/or full LUS (fLUS) thickness were performed in 399 (63%) patients. The incidence, time, and mode of detection of uterine defects were studied. Sensitivity, specificity, positive (PPV) and negative predictive values (NPV) were calculated for different cut-off values of LUS thickness. Uterine defects were diagnosed in 28 (4.4%) patients. Detection rate of ultrasound was low (13.6%), with better sensitivity, specificity, PPV, and NPV at lower (2 mm (fLUS) / 1 mm (mLUS): 75/96/48.3/98.7%) than at higher cut-off values (3 mm (fLUS) / 2 mm (mLUS): 15.8/93.2/10.4/68.7%). The benefit of LUS thickness measurement appears overestimated. As a large number of methodological factors trigger inaccuracy, a consistent protocol including both a transabdominal and a transvaginal scan performed by a trained examiner might improve accuracy. Exclusion of uterine defects might be more useful for prenatal selection after CS.

Sonographic assessment of lower uterine segment thickness at term in women with previous cesarean delivery.

The purpose of this study was to establish the validity of abdominal sonographic evaluation of lower uterine segment (LUS) thickness in full-term pregnancies with a single previous cesarean section, and to assess the usefulness of measuring LUS thickness in predicting the risk of uterine dehiscence. Three hundred and thirty-six women with a single previous cesarean section who had an ultrasound measurement of the LUS thickness in pregnancy were enrolled. Abdominal sonographic assessment of LUS was carried out within 2 weeks of delivery. Sonographic measurements were correlated visual finding of a uterine scar at the time of the iterative cesarean section. Receiver operating curve analyses has been used to determine the detection rate and the risk of each actual value of LUS thickness vs. a thin uterine scar. In our present study, 2.5 mm was considered the critical cut-off value of the LUS thickness. This critical cut-off value was derived from the ROC curve with sensitivity, specificity, PPV, and NPV of 90.9, 84, 71.4, and 95.5 %, respectively (using transabdominal ultrasound). The linear regression model analysis revealed that full LUS thickness of <2.5 mm was the only factor to be correlated with translucent lower uterine segment (C3) (8.8 vs. 0 %; P = 0.02). Full LUS thickness of <2.5 mm is associated with a higher risk of uterine dehiscence.

Uterine Scar Defect at 12 Weeks’ Gestation

A 38-year-old woman with a history of Caesarean section was found to have a large defect in the lower uterine segment (LUS) on ultrasound examination at 12weeks’ gestation. The residual myometrium thickness (RMT) was thin (2.6mm) compared with the full LUS thickness beside the defect (9.0mm). Serial ultrasound examinations at 16, 23, and 33weeks revealed no significant change in RMT (2.8, 4.2, and 3.2mm, respectively). Repeat Caesarean section was performed during labour at 38weeks’ gestation, and no evidence of uterine scar dehiscence was found.

Sonographic Measurement of Lower Uterine Segment Thickness to Predict Uterine Rupture During a Trial of Labor in Women With Previous Cesarean Section

Along with the increasing rate of cesarean section (CS) births has been a concomitant decrease in the rate of vaginal birth after cesarean (VBAC), mostly due to concerns about uterine rupture during a trial of labor (TOL). The risk of uterine rupture in laboring women with a previous CS must be balanced against the increasing current and future risk of peripartum hysterectomy with repeat cesarean. Improved prediction of uterine rupture could allow women at low risk to have a TOL, and those at high risk for uterine rupture could undergo a planned CS. Thinning in the lower uterine segment (LUS) measured by ultrasonography is a possible predictor of uterine rupture. The present study was performed to identify an optimal LUS thickness cutoff value and to define groups of women with a history of previous CS to whom TOL either should not be offered or could be offered safely. PubMed and EMBASE were searched for relevant articles published during 1980 to 2011. Included studies reported on pregnant women with at least 1 prior CS and on the sonographic appearance of the LUS during pregnancy in relation to uterine defects observed during or immediately after delivery. Studies were scored on methodologic and clinical characteristics. For each study, a 2 x 2 table was constructed, cross-classifying LUS thickness measured by ultrasound and the presence of LUS defect after delivery. Sensitivity and specificity were determined for each study in the receiver operating characteristic (ROC) space along with a corresponding summary ROC curve. From an initial 147 citations, 21 studies (all cohort design) were included and involved 2776 women. The median sample size was 71 (range, 10-642; interquartile range, 149.5). Lower uterine segment measurements were obtained at 34 to 39 weeks' gestation. Cutoff values used to define an insufficient LUS ranged from 0.5 to 3.0 mm in studies measuring myometrial LUS thickness and from 1.5 to 5.1 mm in those using full LUS thickness. Full LUS thickness measurement using cutoffs of 2.0 to 3.0 mm had a specificity of 0.91 (95% confidence interval [CI], 0.80-0.96) at a sensitivity of 0.61 (95% CI, 0.42-0.77). Full LUS thickness measurement using cutoffs of 3.1 to 5.1 mm had a specificity of 0.63 (95% CI, 0.30-0.87) at a sensitivity of 0.96 (95% CI, 0.89-0.98). The accuracy of transvaginal or transabdominal sonography could not be compared statistically because of the limited number of studies. The main finding is the strong negative correlation between LUS thickness and risk of uterine defect. The similar shapes of the ROC curves for myometrial and full LUS thickness indicated no significant difference in accuracy, shape, and position. An ideal screening test to predict uterine rupture could affect medical decision making by allowing accurate selection of women with a scarred uterus unlikely to have uterine rupture and thus able to have a TOL

Sonographic measurement of lower uterine segment thickness to predict uterine rupture during a trial of labor in women with previous Cesarean section: a meta‐analysis

To evaluate the accuracy of antenatal sonographic measurement of lower uterine segment (LUS) thickness in the prediction of risk of uterine rupture during a trial of labor (TOL) in women with a previous Cesarean section (CS). PubMed and EMBASE were searched to identify articles published on the subject of sonographic LUS measurement and occurrence of a uterine defect after delivery. Four independent researchers performed identification of papers and data extraction. Selected studies were scored on methodological quality, and sensitivity and specificity of measurement of LUS thickness in the prediction of a uterine defect were calculated. We performed bivariate meta-analysis to estimate summary receiver-operating characteristics (sROC) curves. We included 21 studies with a total of 2776 analyzed patients. The quality of included studies was good, although comparison was difficult because of heterogeneity. The estimated sROC curves showed that measurement of LUS thickness seems promising in the prediction of occurrence of uterine defects (dehiscence and rupture) in the uterine wall. The pooled sensitivity and specificity of myometrial LUS thickness for cut-offs between 0.6 and 2.0 mm was 0.76 (95% CI, 0.60-0.87) and 0.92 (95% CI, 0.82-0.97); cut-offs between 2.1 and 4.0 mm reached a sensitivity and specificity of 0.94 (95% CI, 0.81-0.98) and 0.64 (95% CI, 0.26-0.90). The pooled sensitivity and specificity of full LUS thickness for cut-offs between 2.0 and 3.0 mm was 0.61 (95% CI, 0.42-0.77) and 0.91 (95% CI, 0.80-0.96); cut-offs between 3.1 and 5.1 mm reached a sensitivity and specificity of 0.96 (95% CI, 0.89-0.98) and 0.63 (95% CI, 0.30-0.87). This meta-analysis provides support for the use of antenatal LUS measurements in the prediction of a uterine defect during TOL. Clinical applicability should be assessed in prospective observational studies using a standardized method of measurement.

Measurements of the lower uterine segment during gestation

To establish normal values for the lower uterine segment (LUS) thickness and to recognize factors that may affect these values. In this cross-sectional study, we measured the LUS thickness in women between 11 and 41 weeks gestation. Women with placental abnormalities and fetal anomalies were excluded. Fetal weight, location of placental implantation, and cervical length were estimated. The LUS was examined to identify the thinnest zone and evaluated using the transvaginal approach with an empty urinary bladder. Full LUS thickness was measured with a caliper at the inner surface of the posterior bladder wall and another caliper at the interface between the amniotic fluid and the decidua. The myometrium was measured with the first caliper at the interface between the amniotic fluid and the deciduas and the second between the bladder wall and the myometrium. Normal values for the LUS were established throughout gestation, and correlations between the LUS gestational age, fetal weight, previous cesarean section, and other parameters were examined. Overall, 350 women were included in our study. Median parity was 1 (0-6) and the majority (62%, 218/350) of women have not had a previous cesarean section. The LUS thickness inversely correlated with gestational week (Pearson's r = -0.11, p < 0.03). When stratifying the linear regression model to women with and without a history of a previous cesarean section, it was demonstrated that gestational age was moderately correlated with LUS only in the second group of patients (Pearson's r = -0.16, p = 0.1 and Pearson's r = -0.47, p < 0.0001, respectively). During the post term period, patients who had had a previous cesarean section had significantly thinner LUS compared with patients who had not had a previous cesarean section (46 mm ± 20 versus 59 mm ± 20, p = 0.002, respectively). Neither parity nor the number of previous cesarean sections were found to correlate with the thickness of the LUS (p > 0.05). Multivariate linear regression (R(2) = 0.215, F(2, 63) = 9.021, p < 0.001) demonstrated that both gestational week (β = -0.13, p < 0.04) and cesarean section (β = -0.01, p < 0.0001) were independent factors associated with the thickness of the LUS; for every 1 week increase in gestational week, there was a 1.3 mm decrease in the total thickness of the LUS CONCLUSIONS: We have established reference ranges for LUS thickness throughout gestation. The LUS thickness decreases throughout gestation in singleton pregnancies and is significantly thinner in postterm period pregnant women with a previous cesarean section.

Reliability of 3-Dimensional Transvaginal Sonographic Measurement of Lower Uterine Segment Thickness

The purpose of this study was to report the intraobserver and interobserver reliability of transvaginal 3-dimensional (3D) sonographic measurement of lower uterine segment thickness. A prospective study of 60 pregnant women with previous low transverse cesarean deliveries was performed between 35 and 39 weeks' gestation. Two observers, blinded to the clinical data, independently measured the full lower uterine segment thickness by 2-dimensional (2D) transvaginal sonography. Three-dimensional volume data sets of the lower uterine segment were captured and analyzed more than 2 months later by both observers independently. Intraobserver, interobserver, and intermethod reliability was evaluated by median absolute differences, nonparametric limits of agreement, intraclass correlation coefficients (ICCs), and κ coefficients. The median full lower uterine segment thickness was 3.6 mm (range, 0.9-8.0 mm). Intraobserver reliability (median difference, 0.3 mm [interquartile range (IQR), 0.1-0.6 mm]; ICC, 0.88 [95% confidence interval (CI), 0.81-0.93]; κ, 0.87 [95% CI, 0.69-1.00]) and interobserver reliability (median difference, 0.3 mm [IQR, 0.1-0.5 mm]; ICC, 0.88 [95% CI, 0.81-0.93]; κ, 0.86 [95% CI, 0.66-1.00]) were excellent. Reliability between 3D and 2D sonography was moderate (median difference, 0.6 mm [IQR, 0.2-0.9 mm]; ICC, 0.78 [95% CI, 0.66-0.86]; κ, 0.56 [95% CI, 0.28-0.85]). However, intermethod reproducibility was improved when the full lower uterine segment thickness was less than 3.0 mm (median difference, 0.4 mm [IQR, 0.2-0.9 mm]). Full lower uterine segment thickness measured with 3D transvaginal sonographic data sets has excellent intraobserver and interobserver reliability. It also has good reproducibility with 2D sonography when the full lower uterine segment thickness is less than 3.0 mm.

Reliability of Two-Dimensional Transvaginal Sonographic Measurement of Lower Uterine Segment Thickness Using Video Sequences

To report the intra- and interobserver reliability of measurement of the lower uterine segment (LUS) thickness using transvaginal sonographic videos. A prospective study of 60 women with previous, low-transverse cesarean undergoing LUS examination (36 to 39 weeks) was performed. Two observers independently measured full LUS thickness using transvaginal sonography. A video of the LUS was recorded and analyzed more than 2 months later by both observers. Intra- and interobserver reliability was assessed with median absolute differences and interquartile range (IQR), nonparametric limits of agreement, intraclass correlation coefficients (ICC) with 95% confidence interval (95% CI), and kappa coefficients. Median full LUS thickness was 3.6 mm (range: 0.9 to 8.0 mm). Intraobserver repeatability was excellent (median difference: 0.2 mm, IQR: 0.1 to 0.4; ICC: 0.94, 95% CI: 0.90 to 0.96; kappa: 1.00). Interobserver (median difference: 0.3 mm, IQR: 0.2 to 1.3; ICC: 0.91, 95% CI: 0.86 to 0.95; kappa: 0.76, 95% CI: 0.54 to 0.98) and intermethod reproducibility (median difference: 0.4 mm, IQR: 0.2 to 0.8; ICC: 0.82, 95% CI: 0.72 to 0.89; kappa: 0.69, 95% CI: 0.43 to 0.94) were good. However, both interobserver and intermethod reproducibility were improved when LUS thickness was below 3 mm. Full LUS thickness measured from transvaginal sonographic videos has excellent intra- and interobserver reproducibility and good reproducibility with live transvaginal ultrasound.

Factors Associated With Lower Uterine Segment Thickness Near Term in Women With Previous Caesarean Section

ObjectiveTo estimate the association between potential influencing factors and lower uterine segment (LUS) thickness at term in women with previous Caesarean section. MethodsWe conducted a cohort study of women with previous low-transverse Caesarean section undergoing ultrasonographic measurement of LUS thickness between 35 and 38 weeks’ gestation in a tertiary care centre between 2006 and 2009. Measurements of the full LUS thickness and the myometrial LUS thickness were performed both transabdominally and transvaginally. The thinnest measurements for both full and myometrial LUS thicknesses were considered dependent variables. Non-parametric analyses, multivariate linear regression analyses, and multivariate regression analyses were used to evaluate the relationships between LUS thickness and the potential influencing factors of maternal age, interdelivery interval, prior vaginal delivery, and several characteristics of the previous Caesarean section. ResultsIn 377 women who underwent measurement of LUS thickness, labour before previous Caesarean section was the only characteristic associated with a greater full LUS thickness (an additional 0.9mm; 95% CI 0.5 to 1.2 mm) in multivariate linear regression analysis. Labour before previous Caesarean section (0.5 mm; 95% CI 0.2 to 0.7 mm) and the use of synthetic sutures (as opposed to catgut sutures) for the closure of the previous hysterotomy incision (0.3mm; 95% CI 0.02 to 0.5 mm) were the only two variables significantly associated with a thicker myometrial LUS. In multivariate regression analysis, three factors were predictive of a full LUS thickness of > 2.3mm: the presence of labour, a recurrent indication for Caesarean section, and the use of synthetic sutures for hysterotomy closure at previous Caesarean section (P < 0.05). ConclusionLabour at the time of previous Caesarean section is associated with a thicker LUS near term in the subsequent pregnancy. The use of synthetic sutures for hysterotomy closure is another factor potentially associated with a thicker LUS.

Sonographic Lower Uterine Segment Thickness and Risk of Uterine Scar Defect: A Systematic Review

ObjectiveTo study the diagnostic accuracy of sonographic measurements of the lower uterine segment (LUS) thickness near term in predicting uterine scar defects in women with prior Caesarean section (CS). Data SourcesPubMed, Embase, and Cochrane Library (1965–2009). Methods of Study SelectionStudies of populations of women with previous low transverse CS who underwent third-trimester evaluation of LUS thickness were selected. We retrieved articles in which number of patients, sensitivity, and specificity to predict a uterine scar defect were available. Data SynthesisTwelve eligible studies including 1834 women were identified. Uterine scar defect was reported in a total of 121 cases (6.6%). Seven studies examined the full LUS thickness only, four examined the myometrial layer specifically, and one examined both measurements. Weighted mean differences in LUS thickness and associated 95% confidence intervals between women with and without uterine scar defect were calculated. Summary receiver operating characteristic (SROC) analysis and summary diagnostic odds ratios (DOR) were used to evaluate and compare the area under the curve (AUC) and the association between LUS thickness and uterine scar defect. Women with a uterine scar defect had thinner full LUS and thinner myometrial layer (weighted mean difference of 0.98 mm; 95% CI 0.37 to 1.59, P = 0.002; and 1.13 mm; 95% CI 0.32 to 1.94 mm, P = 0.006, respectively). SROC analysis showed a stronger association between full LUS thickness and uterine scar defect (AUC: 0.84 ± 0.03, P < 0.001) than between myometrial layer and scar defect (AUC: 0.75 ± 0.05, P < 0.01). The optimal cut-off value varied from 2.0 to 3.5 mm for full LUS thickness and from 1.4 to 2.0 for myometrial layer. ConclusionSonographic LUS thickness is a strong predictor for uterine scar defect in women with prior Caesarean section. However, because of the heterogeneity of the studies we analyzed, no ideal cut-off value can yet be recommended, which underlines the need for more standardized measurement techniques in future studies.

Prediction of complete uterine rupture by sonographic evaluation of the lower uterine segment

The purpose of this study was to establish the validity of sonographic evaluation of lower uterine segment (LUS) thickness for complete uterine rupture. A prospective cohort study of women with previous cesarean delivery was conducted. LUS thickness (full thickness and myometrial thickness only) was measured between 35 and 38 weeks gestation, and the thinnest measurement was considered to be the dependent variable. Receiver operating curve analyses and logistic regression were used. Two hundred thirty-six women were included in the study. Nine uterine scar defects (3 cases of complete rupture during a trial of labor and 6 cases of dehiscence) were reported. Receiver operating curve analyses showed that full thickness of <2.3 mm was the optimal cutoff for the prediction of uterine rupture (3/33 vs 0/92; P = .02). Full thickness was also identified as an independent predictor of uterine scar defect (odds ratio, 4.66; 95% confidence interval, 1.04-20.91) Full LUS thickness of <2.3 mm is associated with a higher risk of complete uterine rupture.

OC136: Factors influencing the lower uterine segment thickness in late pregnancies with previous Cesarean Section

Objectives: Several studies have shown that sonographic evaluation of the lower uterine segment (LUS) thickness can predict uterine rupture using either the full LUS thickness or the muscular layer measurement. We aimed to evaluate the potential factors associated with LUS thickness. Methods: A prospective cohort study of women with prior cesarean was conducted. Measurements of the LUS thickness were performed transabdominally and repeated transvaginally if unsatisfactory visualised. The thinnest measurement was considered as the dependant variable. Non-parametric analyses were used to evaluate potential factors associated with LUS thickness including: maternal age, gestational age, interdelivery interval, prior vaginal delivery, and characteristics of the prior cesarean section. Multivariate linear regressions were performed to adjust for confounding variables. Results: 252 women were recruited at a mean gestational age of 36.7 ± 1.3 weeks. In univariate analyses, the only significant factor associated with full LUS thickness was the indication of the prior cesarean (recurrent vs. non recurrent: 3.0 InterQuartile (IQ): 2.4–3.8 mm and 2.5 IQ: 2.0–3.2 mm respectively, P < 0.001). For the muscular layer thickness, the indication (recurrent vs. non recurrent: 1.5 IQ: 1.1–2.1 mm and 1.2 IQ: 0.8–1.8 mm respectively, P < 0.001) and the number of closure layers of the previous cesarean (single vs. double layer : 1.1 IQ: 0.8–1.5 mm and 1.4 IQ: 1.0–1.9 mm respectively, P = 0.02) were significant. The indication of the prior cesarean remained the only significant factor in the linear regression model (P = 0.03). Conclusions: We demonstrated an association between non recurrent indications of prior cesarean and thinner LUS near term. Although this factor has never been associated with higher risk of uterine rupture, we need to consider this information in future researches and analyses of LUS thickness for the prediction of uterine rupture.

OC135: Factors associated with lower uterine segment thickness in women with previous cesarean: A prospective study

Objectives: Several studies have shown that sonographic evaluation of the lower uterine segment (LUS) thickness can predict uterine rupture using either the full LUS thickness or the muscular layer measurement. We aimed to evaluate the potential factors associated with LUS thickness. Methods: A prospective cohort study of women with prior cesarean was conducted. Measurements of the LUS thickness were performed transabdominally and repeated transvaginally if unsatisfactory visualised. The thinnest measurement was considered as the dependant variable. Non-parametric analyses were used to evaluate potential factors associated with LUS thickness including: maternal age, gestational age, interdelivery interval, prior vaginal delivery, and characteristics of the prior cesarean section. Multivariate linear regressions were performed to adjust for confounding variables. Results: 252 women were recruited at a mean gestational age of 36.7 ± 1.3 weeks. In univariate analyses, the only significant factor associated with full LUS thickness was the indication of the prior cesarean (recurrent vs. non recurrent: 3.0 InterQuartile (IQ): 2.4–3.8 mm and 2.5 IQ: 2.0–3.2 mm respectively, P < 0.001). For the muscular layer thickness, the indication (recurrent vs. non recurrent: 1.5 IQ: 1.1–2.1 mm and 1.2 IQ: 0.8–1.8 mm respectively, P < 0.001) and the number of closure layers of the previous cesarean (single vs. double layer : 1.1 IQ: 0.8–1.5 mm and 1.4 IQ: 1.0–1.9 mm respectively, P = 0.02) were significant. The indication of the prior cesarean remained the only significant factor in the linear regression model (P = 0.03). Conclusions: We demonstrated an association between non recurrent indications of prior cesarean and thinner LUS near term. Although this factor has never been associated with higher risk of uterine rupture, we need to consider this information in future researches and analyses of LUS thickness for the prediction of uterine rupture.