Accuracy of first trimester sonographic features in diagnosing caesarean scar pregnancy

Introduction: Caesarean scar pregnancy (CSP), if not managed timely, can result in pre-term labour, postpartum haemorrhage, hysterectomy or maternal and fetal death. This study aims to compare the diagnostic performances of different sonographic features recommended in various good practice recommendations and literature; then propose an algorithm that could aid in easier identification of CSP using transvaginal ultrasound. Methods: A retrospective review of ultrasound images of intrauterine pregnancy (IUP) and CSP between 4.9 and 11.9 weeks gestation was conducted. The diagnostic performance of the Royal College of Obstetricians & Gynaecologists (RCOG) guideline, Timor-Tritsch et al. (TT) method and combined method were evaluated. An algorithm was then created to calculate a numerical value for diagnosis. The methods were tested for intra- and inter-observer agreement. Results: A total of 66 ultrasound cases (30 IUP and 36 CSP) were included in this study. The sensitivity of the RCOG guideline, TT method and combined method were 58.3%, 94.4% and 100% while the specificity were 96.7%, 90% and 90%, respectively. The TT method and combined method performed significantly better than the RCOG guideline (p =.0016 and.0002, respectively). Using the proposed algorithm, a value larger or equal to 52.2 gave 97.2% sensitivity and 93.3% specificity that CSP is present. Intra- and inter-observer agreement for all methods were moderate to almost perfect. Conclusion: Screening during early first trimester is important to improve the diagnostic accuracy of CSP. The TT method is a good supplement to the RCOG guideline. The proposed algorithm is a useful tool to improve diagnostic accuracy and confidence.