3D Ultrasound on Beginning of the 8th Week of Pregnancy

By the beginning of the 8th week, the embryo has develop a skeleton, which is mostly cartilaginous and gives form to its body. The communication between the primitive gut and the yolk sac has been reduced to a relativity small duct (the yolk stalk).

3D ultrasound findings: The most characteristic finding is a complete visualization of the limbs, which end in thicker areas that correspond to the future hands and feet. The shape of the face begins to appear but is not clearly seen. The great majority of embryos show a cranial pole flexion that makes it almost impossible to see the face. Insertion of the umbilical cord is visible on the anterior abdominal wall. During the 8th week of pregnancy, there is expansion of the ventricular system of the brain (lateral, third and midbrain ventricles). Due to these processes, the head erects from the anterior flexion. The vertex is now located over the position of the midbrain. Structures of the viscerocranium are not visible due to their small size. Arms and feet are clearly visible. Insertion of the umbilical cord is visible on the anterior abdominal wall. During the 8th and 9th weeks, the developing intestine is being herniated into the proximal umbilical cord.Blats and coworkers reported on a 7 weeks and 5 days gestational age embryo whose brain structures were analyzed in detail by 3D ultrasound. They described distinct hemispheres how the rhombencephalic cavity (future fourth ventricle) deepens gradually with the growth of the embryos, at the same time decreasing its length. At this time, it has a pyramid-like shape with the central deepening of the pontine flexure as the peak of the pyramid.

3D power Doppler findings: During the 8th and 9th week, developing intestine is being herniated into the proximal umbilical cord, which can be assessed using the technique. By the eighth week, an embryo's length is between 10 and 16 mm, and the CRL is easily measured.