Objective On the basis of retrospectively analysis the trans-cerebellar section showing the Sylvian fissure of normal fetus is better than trans-thalamic section in middle and late trimester, we prospectively established the normal reference range of developmental parameters related to the Sylvian fissure of normal fetus in the trans-cerebellar section in order to provide valuable information for the diagnosis of fetal cerebral cortical dysplasia. Methods A prospective cross-sectional study was

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... conducted on 845 normal fetuses at 21 to 32 weeks of gestation from January 2019 to September 2020. The depth and width of the Sylvian fissure was measured respectively, and regression analysis was performed according to different gestational age groups. Results The depth of Sylvian fissure was positively correlated with gestational weeks, and the width of Sylvian fissure was negatively correlated with gestational weeks, with correlation coefficients 0.751 and 0.825 respectively (all P < 0.001).Taking gestational weeks as the independent variable, and the depth and width of Sylvian fissure of fetus as the dependent variables, linear regression analysis showed that there was a linear relationship between the independent variables and the dependent variables. The obtained equation was simplified to a formula: Fetal Sylvian fissure depth (mm)=7+0.6X(gestational weeks-21), Sylvian fissure width (mm)=8-0.6X(gestational weeks-21). Conclusion The reference range of the depth and width of Sylvian fissure of normal fetus at 21 to 32 weeks of pregnancy through the trans-cerebellar section was established, which could provide valuable information for the evaluation of the normal development of the lateral fissure of fetus and the prenatal diagnosis of fetal cortical hypoplasia. Key words Fetus; Sylvian fissure; depth; width; trans-cerebellar section