Background:Fetal brain development is a complicated process that continues throughout pregnancy.Fetal sulcus development has typical morphological features.Assessment of fetal sulcus development to understand the cortical maturation and development by prenatal ultrasound has become widespread.This study aimed to explore a reliable method to assess cortical sulcus and to describe the normal sonographic features of cortical sulcus development in the human fetus between 18 and 41 weeks of gestation.Methods:A cross-sectional study was designed to examine the fetal cortical sulcus development at 18-41 weeks of gestation.Ultrasound was used to examine the insula,sylvian fissure (SF),parieto-occipital fissure (POF),and calcarine fissure (CF).Bland-Altman plots were used for assessing the concordance,and the intraclass correlation coefficient was used for assessing the reliability.Results:SF images were successfully obtained in 100％ of participants at 22 weeks of gestation,while the POF images and CF images could be obtained in 100％ at 23 weeks of gestation and 24 weeks of gestation,respectively.The SF width,temporal lobe depth,POF depth,and the CF depth increased with the developed gestation.The width of uncovered insula and the POF angle decreased with the developed gestation.By 23 weeks of gestation,the insula was beginning to be covered.Moreover,it completed at 35 weeks of gestation.The intra-and inter-observer agreements showed consistent reproducibility.Conclusions:This study defined standard views of the fetal sulcus as well as the normal reference ranges of these sulcus measurements between 18 and 41 weeks of gestation.Such ultrasonographic measurements could be used to identify fetuses at risk of fetal neurological structural disorders.