Prenatal Age: 4 – 6 Weeks Post-LMP
>2 – 4 Weeks Post-Conception
By 5 weeks, development of the brain, the spinal cord, and the heart is underway. The heart begins beating at 5 weeks and one day and is visible by ultrasound.
By 6 weeks, the heart is pumping blood. All four chambers of the heart are present.
The head, as well as the chest and abdominal cavities have formed and the beginnings of the arms and legs are visible. At 6 weeks, the embryo measures less than ¼ of an inch long.