FundAl Retroflexion (FAR) angle is a novel sonographic marker associated with Cesarean scar pregnancies in the first trimester A case-control study

Objectives Early diagnosis of Cesarean scar pregnancies (CSP) remains difficult. This study describes a novel sonographic marker, the FundAl Retroflexion (FAR) angle, that may be used in the first trimester. The objective of the study is to compare the FAR angle between CSP and normal pregnancies. Methods For this case-control study, we reviewed images from our institution's database that were acquired from January 2016 to December 2019. All cases of CSP and randomly selected controls, defined as patients with history of Cesarean delivery and normal implantation, that underwent ultrasound evaluation at <14 weeks were included. The FAR angle, defined as the acute angle created between the endometrial echo and cervical canal, was measured. The mean FAR angle was then compared between the two groups and a receiver operating characteristic (ROC) curve was generated. Results We identified 15 cases of CSP during the study period and were able to measure the FAR angle in 14 of the cases. The mean FAR angle was larger in CSP than in normal control pregnancies (45 degrees versus 27 degrees, respectively, P < 0.001). Using an ROC curve, a FAR angle cut off of 40 degrees maximizes the ability to distinguish between CSP from normal pregnancies. Conclusions The FAR angle provides an easily obtainable and numerical measurement. CSP have larger FAR angle compared to normal controls with a distinguishing cut off of 40 degrees. Larger studies are needed to determine if using the FAR angle can improve first trimester diagnosis for CSP.