UOG Journal Club: August 2013Sonographic measurement of lower uterine segment thickness to

predict uterine rupture during a trial of labor in women with previous Cesarean section: a meta-analysis

N. Kok, I. C. Wiersma, B. C. Opmeer, I. M. De Graaf, B. W. Mol, E. PajkrtVolume 42, Issue 2, Date: August 2013, pages 132–139

Journal Club slides prepared by Dr Tommaso Bignardi(UOG Editor for Trainees)

Background

• The risk of uterine rupture in laboring women with a previous Cesarean section (CS) varies between 0.2% and 1.5% after induction of labor, compared to 0.5% in women with spontaneous labor after a previous CS.

• Several studies have proposed that thinning of the lower uterine segment (LUS) measured by ultrasonography is a predictor of uterine rupture.

• Accurate prediction of uterine rupture would allow women at low risk to proceed with a trial of labor (TOL), whereas women at high risk for uterine rupture could undergo a planned CS.

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).

Objective

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

Kok et al., UOG 2013

• Studies on pregnant women with at least one previous CS

• Studies that reported on sonographic appearance of LUS during pregnancy in relation to uterine defects observed during or immediately after delivery

• Studies that allowed construction of 2×2 tables comparing LUS

thickness measurement and the occurrence of uterine scar defects (uterine scar dehiscence or uterine scar rupture)

• 1980 – December 2011

Inclusion criteria

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

Kok et al., UOG 2013

• Uterine scar dehiscence: loss of continuity of myometrial layer without complete rupture of LUS

• Uterine rupture: complete separation of the uterine scar resulting in communication between the uterine and peritoneal cavities

• Full LUS thickness: distance between bladder wall and amniotic cavity

• Myometrial thickness: minimum thickness overlying amniotic cavity at the level of uterine scar (only myometrium is measured)

Definitions

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

Kok et al., UOG 2013

Total citations (n = 297) screened for relevance: PubMed (n = 143); EMBASE (n = 150); Reference lists (n = 4)

References excluded because of duplication (n = 150)

Studies excluded because of inappropriate reporting of outcome (n = 10) or language restrictions (n = 3)

Citations retrieved for more detailed evaluation of full manuscripts (n = 34)

Studies included in systematic review (n = 21)

References excluded after screening title (n = 84)

References excluded after screening abstract (n = 29)

• Methodological quality assessment: Quality Assessment of Diagnostic Accuracy Studies (QUADAS) tool

• Data independently extracted by four reviewers

• Data extracted: sonographic LUS thickness during pregnancy (index test), definition of uterine scar defect, full or myometrial LUS measurement, transabdominal or transvaginal measurement, level of experience of ultrasound examiners, number of examiners, number of measurements, gestational age at measurement, a priori determined threshold for LUS thickness, blinding, setting, study population, study design, data collection, number of participants, adverse neonatal or maternal outcome, VBAC success rate and prevalence of a uterine defect

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

Kok et al., UOG 2013

Methods

• For each study a two-by-two table was constructed, cross-classifying LUS thickness measured by ultrasound and the presence of LUS defect after delivery

• A bivariate meta-regression model was used to calculate pooled estimates of sensitivity and specificity and to calculate the corresponding summary ROC (sROC) curve

• Separate sROC curves were calculated for full and myometrial LUS measurements

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

Kok et al., UOG 2013

Methods

Results

Results: characteristics of studies included

NR, not reported; Prosp., prospective cohort; Retro., retrospective cohort; TAS, transabdominal sonography; TVS, transvaginal sonography

ResultsSummary of the Quality Assessment of Diagnostic Accuracy Studies

(QUADAS) tool for articles included

Results: sROC curves (−) and pooled sensitivity and specificity ( ●) for prediction of uterine defects*

Myometrial lower uterine segment (LUS) thickness

Full lower uterine segment (LUS) thickness

*Rectangles show the observed accuracy for each cut-off point in each study

1-specificity 1-specificity

Results

Myometrial LUS thicknesscut-off ranges 0.6–2.0 mm: ○ observed accuracy;● pooled sens/spec; ─ sROC curve2.1–4.0 mm: □ observed accuracy;■ pooled sens/spec; - - sROC curve

Full LUS thicknesscut-off ranges 2.0–3.0 mm: ○ observed accuracy;● pooled sens/spec; ─ sROC curve 3.1–5.1 mm: □ observed accuracy;■ pooled sens/spec; - - sROC curve

1-specificity 1-specificity

• Full LUS thickness measurement between 2.0 and 3.0 mm reached a specificity of 0.91 (95% CI, 0.80–0.96) at a sensitivity of 0.61 (95% CI, 0.42–0.77).

• Full LUS thickness measurement between 3.1 and 5.1 mm reached 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 TVS and TAS could not be compared statistically

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

Kok et al., UOG 2013

Results

• Strong negative correlation between LUS thickness and risk of uterine defect

• Similar ROC curves for myometrial and full LUS thickness, indicating no significant difference in any of the three parameters: accuracy, shape and position

Discussion

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

Kok et al., UOG 2013

• Thorough search without language restrictions

Strengths of the study

Limitations

• Considerable amount of heterogeneity among studies with use of different cut-offs and variable definition of uterine defect

• Large number of small studies (inclined to overestimate the predictive capacity of LUS thickness)

• More than 75% of studies not blinded

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

Kok et al., UOG 2013

Conclusions

• 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.

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

Kok et al., UOG 2013

Discussion points• Do we need a consensus on terms and definitions regarding ‘uterine

defects’?

• What is the clinical significance of a ‘silent’ uterine scar dehiscence?

• Do we need a consensus regarding which layer(s) of the LUS should be measured and by which route?

• What is the agreement on such measurements between different observers?

• Can clinical factors influence the accuracy of this tool?

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

Kok et al., UOG 2013