OC10.08: Prospective evaluation of internal cranial fronto‐occipital diameter/corpus callosum length ratio on normal depistage prenatal ultrasound

French echographic academy include recently obligatory image of corpus callosum (CC). Practitioners regularly wonder if its size is normal, even if its measurement is not requested during screening ultrasound (US). We propose to evaluate feasibility of relationship between internal cranial fronto-occipital diameter (IFOD) and length of CC on the new section of profile/CC easily achievable to know its reliability in a population of normal fetuses and its reproducibility to help. Data was done prospectively from 1 February to 1 March 2023. 118 fetuses were included out of 124 US performed. Patients didn't have hypertension or diabetes. Fetuses were eutrophic, between 18GA (Gestational Age) and 34GA. CC measurement quality criteria were strictly median sagittal section with vermis and IFOD measurement in same axis between internal bone tables. CC biometrics were subjectively estimated to be normal. Biometrics were secondarily controlled normal (> 3rd percentile). IFOD/CC was calculated and evaluated by pregnancy trimester. IFOD/CC was possible on 95.1% of 124 examinations, independently of other biometrics. Overall it was on average 2.51 (+/-0.14): 2.41 in the 3rd trimester (+/-0.12) for 34 patients, 2.55 (+/- 0.13) in the 2nd trimester for 78 patients and 3.2 (+/-0.5) for 6 patients before 21GA. Ratio is substantially proportionally decreasing according to the term of pregnancy. Reproducibility and performance of IFOD/CC is good on fetal depistage US. This method is fast and could be more useful than only charts since it is valid for eutrophic fetuses depending on their trimester. Maybe it could help to avoid biases and diagnoses of CC hypoplasia. This study is continuing retrospectively with archived images whose pregnancy outcomes are known normal. Comparison and relevance of ratio in fetuses with growth-retardation in utero on prenatal US without cerebral malformation and anatomically to assess whether it is transposable during fetal autopsy examinations are currently in progress.