Fetal brain was retrospectively evaluated in 418 normal fetuses at 16–28 weeks of gestation. The multiplanar mode to obtain the axial cerebral plane and measured the width of the cavum septum pellucidum (CSP) and biparietal diameter (BD). All measurements of CSP were done from as the widest diameter across both borders in an inter-to inter fashion. The CSP width is increasing at second trimester of gestation. Normal range plotted on the reference range (mean, 5th and 95th percentiles) of fetal width CSP by measuring of its size may be useful for assessment of fetal brain development in the second trimester of gestation.
