Abstract

Objective: To evaluate clinical significance of lower uterine segment LUS thickness measurement.

Patients and Methods: This prospective study was performed in 2021-2022 in Private Clinic for Obstetric U/S in Baghdad-Iraq, with total of 250 pregnant female, age between 16-45 years. Transabdominal sonographic examination was carried out with a full urinary bladder (to the extent that the patient had the urge to void) to allow good imaging of the LUS and also with empty urinary bladder. The LUS was examined longitudinally and transversely to identify any areas of obvious dehiscence or rupture. Any balloon effect, as described by Michaels et al, consisting of any abnormal bulging of the outer layer associated with fetal movement or changes in amniotic fluid pressure against the urinary bladder base, was noted. If the LUS appeared intact, an attempt would be made to identify the previous uterine scar, and the appearance was noted. The thinnest zone of the lower segment was identified visually at the mid sagittal plane along the cervical canal. This area was magnified to the extent that any slight movement of the caliper would produce a change in measurement by only 0.1 mm. The measurement was taken with the cursors at the urinary bladder wall–myometrium interface and the myometrium/chorioamniotic membrane–amniotic fluid interface. At least 2 measurements were made, and the lowest value was taken as the LUS thickness.

Results: Mean of thickness of LUS when bladder is empty was significantly higher among women aged ≥ 35 years than other younger age groups (3.73 mm, P= 0.001), among those with parity ≥ 5 than other lower parities (3.56 mm, P= 0.045), and in those who delivered by NVD than those who delivered by C/S (3.56 versus 3.05 mm, P= 0.001). No statistical significant difference in thickness of LUS when bladder is empty among those who had different number of previous C/S (P= 0.823). No statistical significant difference in thickness of LUS when bladder is empty among those who had empty or full bladder (P= 0.709). Receiver operating characteristic (ROC) curve analysis was constructed for thickness of LUS when bladder is empty as a predictor for C/S. The cut point of thickness of LUS when bladder is empty was 2.8 mm. Hence, thickness of LUS when bladder is empty < 2.8 mm is predictive for C/S, as a large significant area under the curve (AUC= 68.1%) indicating significant association between lower level of thickness of LUS when bladder is empty and having C/S. Thickness of LUS when bladder is empty was 44.2% sensitive, 90.4% specific, and 61.6% accurate in predicting of C/S. Statistically significant weak positive correlation was detected between thickness of LUS when bladder is empty and BMI level (r= 0.153, P= 0.015).

Conclusion: The LUS thickness as any other organ measurement show variable values according to patient factors including age, BMI and pregnancy related factors including previous NVD or C/S , number of previous C/S , gestational age and parity . The cut off value for LUS thickness in our study 2.8mm found to be highly specific and high positive predictive value for caesarian section, at which this value was close to numerical value reached in previous similar studies.