Abstract
BackgroundPrenatal risk stratification of women with previous cesarean section (CS) by ultrasound thickness measurement of the lower uterine segment (LUS) is challenging. There is a wide range of proposed cutoff values and a valuable algorithm for selection before birth is not available. Using 3 T magnetic resonance imaging (MRI), we aimed to identify possible shortcomings of the current protocols used for birth selection after CS. Therefore, we evaluated anatomic and morphologic differences of the LUS and its thickness in patients with CS and those without. Possible impact factors on LUS thickness were studied.MethodsWe retrospectively analyzed 3 T MRI scans of 164 pregnant women in their second or third trimester, with (patient group, n = 60) and without previous CS (control group, n = 104). Sagittal T2-weighted images were studied. Normal findings of the LUS in MRI, reliability of MRI measurements, as well as factors influencing LUS thickness were assessed. MRI findings were compared to intraoperative findings.ResultsMRI provided good intra- (ICC 0.872) and fair inter-rater reliability (ICC 0.643). The relationship of the LUS and the cesarean scar to the surrounding anatomical structures and also its morphology varied strongly in patients and controls. Scar identification was possible in only 9/60 (15.0%) patients. The LUS was thinner in patients (1.9 ± 0.7 mm) than in controls (2.7 ± 1.3 mm). An LUS thinning up to 1 mm was observed in 23% of women without a previous CS and in 34% of women with normal intraoperative findings. Suspicion of a uterine dehiscence (LUS thickness < 1 mm) was only found in the patient group (5/59 (8.5%)) and was intraoperatively confirmed. In controls, LUS thickness was influenced by fetal weight, gestational age and amniotic fluid amounts.ConclusionVariability in anatomy, thickness and morphology seem to limit common prenatal LUS imaging diagnostics. Therefore, we consider that diagnostic protocols must be re-evaluated and imaging should be adjusted to the individual patient conditions. Due to its independency of ultrasound limitations, an additional MRI might be useful for altered anatomy and impaired ultrasound conditions. An LUS thinning up to 1 mm might be a normal finding and should be further investigated as reference value.
Highlights
Prenatal risk stratification of women with previous cesarean section (CS) by ultrasound thickness measurement of the lower uterine segment (LUS) is challenging
We hypothesize that the current protocols are insufficient but might be improved if specific characteristics of the LUS would be considered in diagnostics
Thereby we aimed to study if thickness measurement by magnetic resonance imaging (MRI) is possible to differentiate a pathologic uterine thinning due to a uterine dehiscence from a ‘normal’ pregnancy related LUS thinning
Summary
Prenatal risk stratification of women with previous cesarean section (CS) by ultrasound thickness measurement of the lower uterine segment (LUS) is challenging. Despite its low incidence of 0.4–0.9% but in consideration of its devastating outcome, risk stratification by additional prenatal ultrasound diagnostics of the lower uterine segment (LUS) has been a hot topic for the last 20 years [3,4,5]. A correlation between LUS thickness and the risk for uterine rupture can be assumed, but neither useful reference values nor even the benefit of prenatal LUS thickness measurement have been clearly demonstrated [4, 6]. The inconsistent results with wide-ranging reference values for the very thin structure of the LUS and experience from clinical routine raise reasonable doubts about the usefulness of LUS thickness measurement for birth selection in clinical practice [10]. We hypothesize that the current protocols are insufficient but might be improved if specific characteristics of the LUS would be considered in diagnostics
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