Cesarean Scar Pregnancy Spectrum: A Proposed Standardized Classification and Terminology for the Reporting of Pregnancy Developing in Uterine Cesarean Scar

Pregnancies after a cesarean delivery (CD) are at risk of blastocyst implantation on uterine scar tissue, resulting in cesarean scar pregnancies (CSPs). CSPs vary in presentation, with severe forms associated with increased risk of placental accreta and myometrial thinning that can resemble ectopic pregnancy. Despite differences in presentation, morbidity, and clinical management across this spectrum, there is controversy regarding their classification. This opinion article proposes a classification system for CSPs modeled after placental accreta spectrum (PAS) to improve patient counseling, clinical planning, and collaborative care. The authors first review the historical development of identification and terminology for pregnancies implanted in the lower anterior uterine segment at the site of previous CDs. Since early investigations beginning in 1924, numerous terms have been proposed as understanding of the pathophysiology evolved. Two terms ultimately emerged: cesarean scar pregnancy and cesarean scar ectopic pregnancy (CSeP). Recent publications have sparked academic debate over whether CSP or CSeP is the more appropriate term, and the authors of this article propose a standardized spectrum called the cesarean scar pregnancy spectrum (CSPS). Modeled after PAS, this framework defines on-the-scar CSP (oCSP) as implantation on a well-healed scar with a residual myometrial thickness (RMT) ≥3 mm, and CSeP as implantation within a large niche with RMT <3 mm, resulting in development outside the normal uterine cavity. Prior research suggests significantly better outcomes for oCSP than for CSeP, supporting the clinical relevance of this distinction. The authors argue that this classification would have multiple benefits, including medically accurate nomenclature, improved counseling and planning for patient safety, compliance with legal and ethical requirements surrounding pregnancy termination, and greater standardization across professional societies. Overall, this opinion article supports adoption of a standardized classification system that distinguishes relatively benign cases of CSPs from those at higher risk for adverse outcomes. Using clearly defined categories such as oCSP and CSeP could shift the discussion away from academic debate and toward standardized screening and management practices that enhance patient safety and comply with legal and ethical standards. (Abstracted from J Ultrasound Med. 2025;9999:1–10. doi:10.1002/jum.70034)