Abstract
There has been an increased prevalence of caesarean deliveries in recent years, leading to a corresponding rise in complications in subsequent pregnancies. Early identification of these complications enables the development of bespoke management approaches which involves adequate preparation and appropriate preoperative planning, which ultimately improves patient outcomes. Ultrasound is the modality of choice in antenatal care for monitoring the fetus and screening for potential pregnancy complications. This thesis contains a collection of 7 publications centred on the role of ultrasound in detecting patients at risk of a complex caesarean section with a particular focus on the risk of uterine rupture during vaginal birth a\er a previous caesarean (VBAC)(Paper 1), differentiation between placenta accreta spectrum (PAS) and uterine scar dehiscence(Papers 2 – 6), as well as discussing important diagnostic pitfalls and challenges of ultrasound assessment for women at high-risk of PAS (Paper 7).Paper 1 evaluated the accuracy of transvaginal measurement of the lower segment thickness in comparison with intraoperative findings, as well as its role in predicting intrapartum uterine scar defects (uterine rupture/dehiscence) in a low resource setting. The study findings revealed a high rate of VBAC failure in cases where the myometrial lower segment thickness was < 2 mm. This measurement demonstrated a high predictive accuracy for uterine defects, with a sensitivity of 91.7% (95% CI: 61.5–99.8%) and a specificity of 81.8% (95% CI: 75.8–86.8%) among those that underwent a caesarean delivery. The state of the lower segment among those with a successful vaginal birth was unknown.
Papers 2 to 6 investigated the utility of ultrasound in differentiating non-PAS uterine scar dehiscence from PAS. These papers revealed novel findings that enhanced our understanding of the diagnostic ability of ultrasound in differentiating these conditions. Papers 2 and 3 were case report and case series papers that described sonographic features observed in patients with scar dehiscence with underlying non-adherent placenta. These papers highlighted sonographic patterns worth exploring in a larger patient cohort. Paper 4 was a retrospective cohort study that demonstrated that, robustly developed PAS diagnostic scoring systems are effective in differentiating high-grade PAS from non-PAS scar dehiscence but not low-grade PAS. Paper 5 revealed that features of lower segment remodeling are
common in both non-PAS uterine scar dehiscence and high-grade PAS, however, features of abnormal vascularity (uteroplacental vascular remodeling and serosal hypervascularity) are unique to high-grade PAS. Relying on these features gives a high diagnostic accuracy in differentiating these two conditions. Paper 6 further demonstrated that state-of-the-art three-dimensional volume rendering ultrasound in modern systems enhances the ability to differentiate between these conditions. This advanced imaging approach offers a more detailed analysis of the uteroplacental interface, which cannot be comprehensively assessed using traditional two-dimensional ultrasound.
These publications constitute a substantial body of novel evidence in the prenatal ultrasound assessment of patients at risk of a complex caesarean section. The findings when externally validated could directly influence practice guidelines worldwide.
| Date of Award | 18 Nov 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Jason Oakley (Supervisor), Collins Sally (Supervisor) & Rebecca Stores (Supervisor) |