Banerjee, Amrita; (2025) Transvaginal ultrasound assessment of full dilatation caesarean section scar characteristics in pregnancy and prediction of spontaneous preterm birth. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Background: Previous term (³37 weeks’ gestation) full dilatation cesarean delivery (FDCD) is associated with an increased risk of subsequent spontaneous preterm birth (sPTB). My primary aim was to develop a protocol to evaluate the caesarean delivery (CD) scar characteristics by transvaginal ultrasound in pregnant women with previous term FDCD and identify the CD scar characteristics that are associated with cervical length shortening and sPTB. Methods: Firstly, I developed a standardised reproducible transvaginal ultrasound protocol to assess CD scar characteristics during the second trimester of pregnancy. I then undertook a prospective cohort study assessing FDCD scar characteristics and developed multiparameter models for prediction of sPTB and shortening cervical length. I performed a systematic review to evaluate all literature on transvaginal ultrasound assessed CD scar characteristics and prediction of adverse obstetric outcomes. I also assessed scar characteristics following advanced-labour first stage CD (ALCD) and previous preterm FDCD (p-FDCD). Results: The reproducibility study showed high real-time two-dimensional interobserver agreement for scar visibility and niche presence, kappa coefficient 0.84 and 0.85, respectively. Scar distance to internal os was the most reproducible measurement. In the prospective cohort FDCD study; CD scar visualisation was 90.5% (220/243), sPTB rate was 4.1% (10/243) and 12.8% (31/243) shortened cervical length. A CD scar within the cervix or <5.0mm above internal os was associated with increased risk of shortening cervical length and/or sPTB (aOR 12.7, p£0.0001). In women with previous ALCD, the scar was less likely to be below the internal os compared to FDCD, (0% versus 15.1%, p=0.011). Recurrent sPTB was significantly more common following previous p-FDCD, 38.1% (8/21) compared to previous preterm vaginal birth, 16.7% (18/108) or preterm CD at <10cm cervical dilatation, 15.3% (17/111); RR 2.3 (p=0.037) and RR 2.5 (p=0.029), respectively. Previous p FDCD scar was located very close to the internal os (<5mm above or below it) in 76.9% (10/13) compared to 33.5% (67/200) following term FDCD, p=0.003. The systematic review showed a paucity of evidence correlating CD scar characteristics and risk of subsequent sPTB. Conclusion: FDCD scar characteristics and distance from internal os can be assessed with a high level of reproducibility during pregnancy and can predict women at risk of sPTB and shortening cervical length.

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