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Short oral presentation abstractsgestation. The 3D volumes were segmented using a previously developed automatic atlas-based segmentation algorithm guided by manual landmarks and US-specific image features (image 1). After visual inspection, individual meshes were automatically generated, rescaled and aligned. A statistical shape model was estimated to describe morphological variability within a common framework (image 2). Results: The model was able to provide a morphological reference that included the normal shape variability (image 3) with green and yellow highlighting areas with greatest variance and to simulate the average longitudinal changes, corrected for size, observed in the healthy fetal population (image 4). Conclusions:We demonstrate that a 3D shape model can be extracted from a 3D US volume allowing objective quantification of craniofacial morphology and determine a reference for the healthy population. If facial morphological differences in genetic conditions can be isolated as distinct from normal faces, this may provide an objective means to diagnose in-utero abnormalities from 3D US scans.

Oral communication abstractsResults: After exclusions, 18,299 pregnancies were available for analysis [BJ1] [KAM2]. Seven cases of 45,X were confirmed in the cohort including 4 with mosaicism, for a prevalence of 1:2614. cfDNA identified 6/7 cases (sensitivity=85.7%). cfDNA results reported high risk for 45,X in 24 cases; 6 of these were confirmed (PPV=25.0%). The updated algorithm did not return a result in 1 affected case, the sensitivity and PPV did not significantly change (83.3% and 33.3%). In 4/7 cases discordance was noted between confirmatory diagnostic tests, summarised in table 1. Conclusions: The prevalence of 45,X was 1:2614, consistent with historical data. The sensitivity of cfDNA was high, despite 4/7 cases with mosaicism. The high rate of discordance between diagnostic tests challenges providers to re-evaluate guidelines for evaluation of high risk cfDNA results for 45,X.