Now that the embryo has implanted itself, it will begin producing the hormone
called "Human Chorionic Gonadotropin," or hCG. It is the hCG that
pregnancy tests detect, showing proof positive that you are expecting!
Your baby is still smaller than a grain of rice, yet somites are beginning to
emerge, forming what will be the spinal column. Disks appear that will
later become the eyes.
Miraculously, only 21 to 23 days into your pregnancy, a
tiny heart begins to beat. Although the vascular system is not fully
developed, the pumping of the heart is pushing fluid throughout the body.
The neural tube closes and the embryo's ears and eyes are in the early stages of
development. Pictures of your baby would show a curved body with a newly
developing head, neck and spinal cord. By week 28, the primitive kidneys,
or mesonephic, has already begun filtering for the body. Your baby's
prominent systems are already developing.
At four weeks, you may be feeling morning sickness in full force. This
is not limited to the morning, and may only last a short period of time or
continue throughout your pregnancy. It is important to keep something in
your stomach, despite any nausea you may feel. The emptier your stomach
is, the worse you may feel.