At 6th Weeks of Gestation

 The embryo has a C-shaped curve. The growth of the head (caused the rapid development of the brain) exceeds that of the other regions.

3D ultrasound findings: Rounded bulky head and thinner body characterize 3D image of an embryo during the 6th week of pregnancy. The head is prominent due to the developing forebrain. Limb buds are rarely visible in this stage of pregnancy. However, umbilical cord and vitelline duct are always clearly seen. At 6th weeks of gestation, ductus omphalomesentricus can be as much as three to four times the length of the embryo itself. The amniotic membrane is also visible, initially at the dorsal part of the embryo. A few days later, it surrounds the embryo but not the yolk sac, which remains in the extracelomic cavity.

3D power Doppler findings: Aortic and umbilical blood flow is well depicted. Initial branches of the umbilical vessels are visible at the placental umbilical insertion. 3D power Doppler detects embryonic heartbeats as early as five weeks and four days menstrual age, at the embryo CRL of 3 + 4 mm. At this very early stage, this finding may help clinicians to diagnose the viability of the pregnancy. Near the end of the sixth week, first signs of aortic and umbilical blood flow within the embryo’s trunk are visible. The initial branches of the umbilical vessels are visible at the pacental umbilical insertion.