UOG Journal Club August 2013 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 N. Kok, I. C. Wiersma, B. C. Opmeer, I. M. de Graaf, B. W. Mol and E. Pajkrt Link to the article (open access) http://onlinelibrary.wiley.com/doi/10.1002/uog.12479/abstract

1. UOG Journal Club: August 2013
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
N. Kok, I. C. Wiersma, B. C. Opmeer, I. M. De Graaf, B. W. Mol, E. Pajkrt
Volume 42, Issue 2, Date: August 2013, pages 132–139
Journal Club slides prepared by Dr Tommaso Bignardi
(UOG Editor for Trainees)

2. 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.

3. 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

4. • 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

5. • 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

6. 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)

7. • 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

8. • 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

9. Results
Results: characteristics of studies included
NR, not reported; Prosp., prospective cohort; Retro., retrospective cohort; TAS, transabdominal
sonography; TVS, transvaginal sonography

10. Results
Summary of the Quality Assessment of Diagnostic Accuracy Studies
(QUADAS) tool for articles included

11. 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

12. Results
Myometrial LUS thickness
cut-off ranges
0.6–2.0 mm: ○ observed accuracy;
● pooled sens/spec; ─ sROC curve
2.1–4.0 mm: □ observed accuracy;
■ pooled sens/spec; - - sROC curve
Full LUS thickness
cut-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

13. • 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

14. • 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

15. • 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

16. 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

17. 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