At week 21 the baby is about 7 inches long and about 11 ounces, it is growing rapidly and continues to move more and more. The feeling of movement continues to get stronger and more obvious. At this point in pregnancy don’t be worried if you do not feel the baby every day, there will be some days where the baby is very obvious and others less so.
At week 21 the baby is swallowing more and more amniotic fluid. This is very important for the gastrointestinal tract as well as the urinary tract. The baby swallows amniotic fluid. This fluid gets digested by the stomach and intestines. It is filtered by the kidneys and forms urine. The urine moves through the urinary tract and finally comes out as amniotic fluid to be swallowed again. This cycle is an important part of the development and growth of these systems as well as helping the muscles involved to strengthen.
At week 21 the movements of the baby are more coordinated. As the brain continues to develop the baby’s movements become less random and more coordinated. These movements are becoming coordinated and purposeful at 21 weeks.
The bone marrow in the baby is starting to function and produce blood cells. As adults most of our blood is made in the bone marrow. For a fetus before week 21 the blood is formed primarily by the liver and other organs. At week 21 the bone marrow is now starting to function and take over the job of blood cell creation. The bone marrow will be the primary site of new blood cells from her on through the life of the baby.