Classification of brain variants on fetal ultrasound: international Delphi consensus

OBJECTIVE: To develop an expert consensus classification and management framework for fetal-brain variants identified on prenatal ultrasound across all trimesters of pregnancy that cannot be categorized confidently as either benign or pathological. METHODS: A two-round international Delphi survey was conducted among experts in fetal medicine and neurosonography, with survey data collected between September 2025 and March 2026. Forty-eight fetal-brain variants, identified through a scoping literature review of PubMed/MEDLINE from database inception to August 2025, performed between June and August 2025, and illustrated with representative ultrasound images, were evaluated. Brain variants were classified according to clinical significance and recommended management into three predefined categories: 'green' (benign variants requiring no additional investigation or follow-up), 'orange' (requiring neurosonographic follow-up) and 'red' (requiring dedicated neurosonography, fetal-brain magnetic resonance imaging and/or genetic investigations). Consensus was predefined as ≥ 70% agreement. In Round 2, experts confirmed their agreement regarding categorization of variants that had reached consensus in Round 1 and reassessed variants that did not reach initial consensus. RESULTS: Forty-eight experts from 14 countries participated in Round 1 and 39 (81.3%) completed both rounds. Of the 48 evaluated variants, 35 (72.9%) reached consensus after two rounds: 12 were classified as 'green', seven as 'orange' and 16 as 'red'. Green variants included isolated choroid plexus cysts < 10 mm across all trimesters, regular asymmetry of the choroid plexuses, isolated cavum septations, cavum vergae, cavum velum interpositum, isolated small cavum septi pellucidi with intact corpus callosum and dolichocephaly with normal head circumference and normal brain morphology. Orange variants included isolated enlargement of intracranial translucency with preserved anatomy, large or bilateral choroid plexus cysts, isolated enlargement of subarachnoid spaces without compression and isolated cyst of the cavum septi pellucidi. Red variants included abnormal posterior fossa markers (loss of normal three-space anatomy, increased brainstem-vermis angle, reduced brainstem-occipital bone distance), periventricular cysts associated with adjacent white-matter abnormalities, thickened corpus callosum and distortion of the interhemispheric fissure, among other findings. Thirteen (27.1%) variants failed to reach consensus, highlighting persistent uncertainty in interpreting subtle isolated asymmetries and selected cystic variants. CONCLUSIONS: This international Delphi consensus proposes an initial expert-derived classification of commonly encountered feta-brain variants on ultrasound. Because the classification has not been validated against postnatal imaging or neurodevelopmental outcomes and reproducibility has not been assessed, prospective evaluation is required before it can be applied in routine practice.