Fetal Stage Development
Development during pregnancy is divided into multiple stages. The second stage, which begins in week eight of pregnancy, is the fetal stage. In this stage of growth, the fetus is more protected than the embryo was, but the fetus is still connected to the mother by the umbiclical cord and encased by the placenta to get oxygen and nutrition. During this stage, amniotic fluid continues to surround the fetus amd absorb shocks.
This stage of development, week eight to week 38, has a significantly decreased risk of miscarriage.
Muscle Development
The fetal stage is where most movement starts. At the beginning of the stage, the frame of bone structures is in place, including the head, brain, hands, feet and organs. During this stage, these grow and develop as new structures like the liver and nervous system form.
By week nine, the fetus can move its arms, head, lungs and hands. Movements, both elicited and spontaneous, are needed for the muscles and body structures to develop correctly. The amniotic fluid continues to provide the fetus with nutrition.
Paper-thin muscles begin to form between week eight and week 15 under translucent skin. During this time frame, red blood cells are produced, the liver forms, limbs lengthen, and the first hairs are developed.
Between week 16 and week 25, expediated muscle development starts with the formation of air sacs in the lungs, eye brows, fingernails, eyelashes and toenails. The nervous system develops and begins to regulate body movement. The nerve part of the ear begins to develop around week 18, and the respiratory system starts regulation.
Body fat and muscle development continues until week 35. By then, the fetus has sensory input and fully developed bones, and produces increased levels of iron, calcium and phosphorus. The lungs continue to develop,
At week 35, a fetus is fully developed and should have the necessary organs to exist outside the mother.
Embryo Stage
The first muscular development, though, happens during the embryonic stage. This stage is typically week one to week eight. During the first eight weeks, the embryo develops the essential structures including the brain, spinal cord, spleen, arms, legs, sensory organ cavities and fingers and toes.
By the time an embryo leave this stage to become a fetus, all major organs should have begun formation.
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