At 21 weeks, each of the babies are a little more than 7 inches long, or the length of a carrot. The period of rapid growth is now slowing. The amniotic fluid that has cushioned and supported our babies in the uterus now serves another purpose. The intestines have developed enough that small amounts of sugars can be absorbed from the fluid that is swallowed and passed through the digestive system to the large bowel. Almost all of the baby's nourishment, however, still comes from me through the placenta.
Until now the baby's liver and spleen have been responsible for the production of blood cells. But now the bone marrow spaces are developed enough to contribute to blood cell formation as well, and bone marrow will become the major site of blood cell production in the third trimester and after birth. (The spleen will stop producing blood cells by week 30, and the liver will stop a few weeks before birth.)
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