Anemia is a condition of too few red blood cells, or a lowered ability of the red blood cells to carry oxygen or iron. Tissue enzymes dependent on iron can affect cell function in nerves and muscles. The fetus is dependent on the mother's blood and anemia can cause poor fetal growth, preterm birth, and low birth weight. In pregnancy, a woman's blood volume increases by as much as 50 percent. This causes the concentration of red blood cells in her body to become diluted. This is sometimes called anemia of pregnancy and is not considered abnormal unless the levels fall too low.
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