Objectives: The purpose of this study was to demonstrate the normal perimeter and area of the three orthogonal planes (axial, sagittal and coronal) of the fetal Sylvian fissure along pregnancy using 3-dimensional (3D) ultrasound. Methods: Ultrasound volumes of fetal head were acquired prospectively in 55 fetuses between 12 and 33 gestational weeks. All volumes were analyzed offline by two examiners separately. The largest axial, sagittal and coronal planes of the Sylvian fissure were identified, and the area and perimeter were measured. Results: Measurements of the Sylvian fissure were demonstrated in 54 out of 55 volumes (98%). In all three planes, a linear growth was demonstrated along gestation. All measurements significantly correlated to gestational age and head circumference (p<0.01). The Sylvian fissure was found to grow asymmetrically, more at the anterior-posterior direction than laterally or to the inferior-superior directions. Conclusions: The Sylvian fissure grows linearly and has a distinct form in each developmental stage. The fissure is identifiable and measurable as early as 12weeks gestation.