The septum pellucidum is the name given to a structure in the fetal brain. The absence of the septum pellucidum during an ultrasound during pregnancy indicates a structural abnormality in the fetal brain, which is commonly associated with abnormalities in fetal intelligence or sensory perception, and requires further testing to confirm the diagnosis. Transparent septal cavity is ultrasound results is an important structure of the fetal brain, in pregnancy ultrasound examination, found that the fetal transparent septal cavity disappeared, need to do further fetal cranial MRI, if necessary, need to draw amniotic fluid for chromosome examination, in order to determine the existence of chromosomal abnormalities in the fetus. The loss of septum pellucidum is mostly seen in abnormal development of the fetal brain center or mental retardation, which requires medical treatment as soon as possible.