e significantly different between the two study groups. We also demonstrated that mLUS and fLUS thickness in women with a prior CD were strong predictors for uterine rupture or uterine dehiscence according to univariate analysis, with cutoff values of 0.97 and 3.13 mm, respectively, where mLUS and fLUS thickness were found to be almost equivalent
Figure 2. LUS thickness and LUS grade prediction by receiver operating characteristic analysis.
Table 5. mLUS and fLUS thickness and LUS grade.
Sensitivity 75.0%, specificity 91.4%, PPV 46.2%, NPV 97.4%
mLUS: myometrial lower uterine segment; fLUS: full thickness lower uterine segment.
assessed by AUC of receiver operating characteristic analysis. In our study, measuring the mLUS, which is more technically difficult, did not add anything to the positive predictive value. The range of error during the sonographic measurement must be minimized because many factors can affect the LUS measurement (contractile state of the uterus, displacement of amniotic fluid, fetal movement and position, operator’s pressure through the transducer during the examination, and fullness of the bladder)  . Measuring only fLUS may be sufficient in estimating the risk of uterine dehiscence. However, the study had several limitations. First, it was a small cohort study and could have led to type 2 errors. A second limitation was that it might not be possible to analyze interactions between risk factors with only 8 cases of LUS grade III/IV observed.
Dehiscence of the LUS is a life-threatening event. Previous studies have found that patients with an LUS thickness of 2.5 or 3.5 mm nave the highest risk of uterine rupture    . LUS thickness greater than 4.45 mm was found to be protective against uterine rupture  . Recent research demonstrated that LUS thickness less than 2.3 mm is associated with a higher risk of complete uterine rupture  . To date, two meta-analyses of LUS measurement have been published. Jastrow et al.  conducted a meta-analysis of 12 articles on LUS thickness and risk of uterine scar defect and showed a strong association between the degrees of LUS thinning and the risk of uterine defects. Kok et al.  in their meta-analysis of 21 studies reported that a full LUS thickness cutoff of 3.1 - 5.1 mm and a myometrium thickness cutoff of 2.1 - 4.0 mm provided a strong negative predictive value for the occurrence of a defect during TOLAC. A myometrium thickness cutoff between 0.6 and 2.0 mm provided a strong positive predictive value for the occurrence of a defect. However, an ideal LUS thickness cutoff value that could be used in clinical practice in women with a scarred uterus could not be defined by these two meta-analyses because of the heterogeneity of the studies. Another concern was that the many small studies were inclined to overestimate the prediction  , which is the case with our study. Furthermore, there were various definitions of uterine defects among the studies, ranging from thinning to complete rupture. Another important factor was that there was no consensus among the studies regarding which layers of the LUS should be measured, or by which route, transabdominal or transvaginal. Consequently, large cohort studies are absolutely necessary in which the LUS measurements are not disclosed to the attending physicians until after the delivery.
We observed six cases of LUS grade III and two cases of LUS grade IV, where seven cases had less than cutoff value of mLUS and six cases had less than cutoff value of fLUS. Contradictory to other studies, all cases of LUS grade III or IV occurred when the interpregnancy time from the most recent previous CD was more than 18 months  - . This time was reported to be the minimum time necessary for adequate activation and for completion of a slow healing process  . However, there were only eight cases with an interpregnancy time of less than 18 months in our study population, and a large number of retrospective studies showed that a short time interval was not a risk factor for major maternal and neonatal complications such as uterine rupture  .
An ideal screening test to predict uterine dehiscence would require high levels of both sensitivity and specificity (≥90%). If such a test were to become available, it is very likely that this would influence medical decision- making, through the accurate selection of women with a previous CD unlikely to have uterine rupture and therefore suitable for a TOLAC, as opposed to women with a previous CD likely to have a uterine rupture and therefore suitable for repeat CD. Sonographic measurements of LUS at term may be a feasible and reliable method to predict uterine rupture or uterine dehiscence in women with a prior CD.
Cite this paper
TadatsuguKinjo,HitoshiMasamoto,KeikoMekaru,YusukeTaira,YukikoChinen,HayaseNitta,YoichiAoki, (2016) Measurements of the Lower Uterine Segment at Term in Women with Previous Cesarean Delivery. Open Journal of Obstetrics and Gynecology,06,1-7. doi: 10.4236/ojog.2016.61001
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