Transvaginal high-resolution ultrasound and three-dimensional (3D) ultrasound have been establishing sonoembryology as well as neurosonography in the first trimester. Fetal brain is rapidly developing and changing its appearance week by week during pregnancy. The most important organ, but it is quite hard to observe detailed structure of this organ by conventional transabdominal sonography. It is possible to observe the whole brain structure by magnetic resonance imaging in the post half of pregnancy, but it is difficult in the first half gestation, and transvaginal high-resolution 3D ultrasound is the most powerful modality. As for brain vascularization, main arteries and veins have been demonstrated and evaluated in various CNS conditions. Transvaginal high-resolution 3D ultrasound can demonstrate cerebral fine vascular anatomy, such as medullary vessels and it is greatly expected to estimate neurological prognosis relating with vascular development during fetal period.