Aim: Septum pellucidum is a thin membrane with right and left leaves, and cavum septum pellucidum (CSP) is formed in the intermembrane region. This study investigates CSP nomogram dimensions for all trimesters in the Turkish population. In addition, the relationship between fetal Doppler flow and CSP size was investigated in this study.Material and Method: This study was designed as a prospective cohort between 2019-2020. Pregnant women between 19-42 weeks who were followed up at University of Health Sciences Tepecik Training and Research Hospital, Department of Obstetrics and Gynecology were included in the study.Results: A total of 517 fetuses meeting our criteria were included in this prospective study. In the second trimester (19-28 weeks) CSP width (4.12±0.88 vs. 4.91±1.42, p