S.L. Collins 1,2, S. Zamudio3, N.P. Illsley3, A. Al-Khan3, & L. Impey2 1 The Nuffield Dept. of Obstetrics & Gynaecology, University of Oxford, Oxford, UK 2 The Fetal Medicine Unit, John Radcliffe Hospital, Oxford, UK 3 Div. of Maternal-Fetal Medicine & Surgery, Hackensack University Medical Center, New Jersey, USA Developing a quantitative scoring system to assess the clinical severity of the abnormally invasive placenta (AIP)  The problem: AIP research and establishment of best practices is hampered by an inability to control for disease severity; most publications lump all degrees of AIP together for analytical/reporting purposes AIP is a heterogeneous (accreta, increta, percreta), life-threatening pathology (10% maternal mortality). AIP severity (i.e. the clinical risk posed to the mother) depends on many factors (placental location, size, depth of invasion, etc.) The more severe the AIP is perceived to be at antenatal diagnosis, the more resources will be employed to decrease the anticipated blood loss. Consequently, it is the small, undiagnosed AIPs which tend to bleed the most. This reflects lack of preparation rather than pathological severity. Our goal: to develop a severity scoring system. Score components: surgical findings (OxGAIP; Figure 2), estimated blood loss (EBL), collateral surgical damage and pathologists' final diagnosis. Corrects for methods used to reduce EBL and for the increased EBL expected for praevias. Our score (OxAIPS; Figure 1) was compared with the gold-standard for severity: expert opinion Methods: Members of the European Working Group on AIP (clinicians with significant experience in AIP) ranked 5 cases of AIP in order of perceived clinical severity. Their expert opinion was compared to the order generated by the numerical OxAIPS system. The OxAIPS score was also calculated for 27 prospectively collected cases. The scores for those who required hysterectomy was compared with those who did not using the Mann-Whitney test. Results: Twelve ‘experts’ rated the five cases. All but one rated them in the same order as the composite OxAIP score (Figure 3). The one who did not merely changed the position of the middle two which were also most numerically similar on the scoring system. The OxAIP scores were significantly higher for women requiring hysterectomy (p<0.001) (Figure 4). Conclusions: The OxAIPS numerical score reflects expert opinion on the clinical severity of AIP. The OxAIPS score was lower in cases not requiring hysterectomy, a surrogate measure of severity. Figure 1: Oxford AIP Severity (OxAIPS) score a OxGAIP grade 1 to 6 (see Figure 1) b Total EBL (in litres) c Pelvic arterial occlusion during CS (no = 1, yes = 1.66) d Number of trips to theatre (including repair of collateral damage e.g. bladder trauma) e Placenta praevia major (no=1, yes = 0.8) f Histopathological diagnosis (Not evidence of AIP=1, Focal accreta=1.4, accreta=1.6, increta 1.8, percreta=2) OxAIPS = (a x b x c x d x e x f) Figure 3 Figure 4 NB Full details of the cases used are available on request from the author. Please email sally.collins@obs-gyn.ox.ac.uk Figure 2: The Oxford Grade of Abnormally Invasive Placenta (OxGAIP)