Anemia is a significant maternal problem during pregnancy. The Centers for Disease Control and Prevention defines anemia as a hemoglobin concentration of < 11 g/dL (hematocrit of < 33%) in the first or third trimester or a hemoglobin concentration of < 10.5 g/dL (hematocrit < 32%) in the second trimester. A pregnant woman will lose blood during delivery and the puerperium, and an anemic woman is at increased jeopardy of blood transfusion and its related complications.
During pregnancy, the blood volume increases by approximately 50% and the red blood cell mass by approximately 33%. This relatively greater increase in plasma volume results in a lower hematocrit but does not truly represent anemia.
Anemia in pregnancy most commonly results from a nutritional deficiency in either iron or folate. Pernicious anemia due to vitamin B12 deficiency almost never occurs during pregnancy. Other anemias occurring during pregnancy include anemia of chronic disease; anemia due to hemoglobinopathy; immune, chronic (eg, hereditary spherocytosis or paroxysmal nocturnal hemoglobinuria), or drug-induced hemolytic anemia; and aplastic anemia.
1. Iron Deficiency Anemia
Iron deficiency is responsible for approximately 95% of the anemias during pregnancy, reflecting the increased demands for iron. The total body iron consists mostly of (1) iron in hemoglobin (approximately 70% of total iron; approximately 1700 mg in a 56-kg woman) and (2) iron stored as ferritin and hemosiderin in reticuloendothelial cells in bone marrow, the spleen, and parenchymal cells of the liver (approximately 300 mg). Small amounts of iron exist in myoglobin, plasma, and various enzymes. The absence of hemosiderin in the bone marrow indicates that iron stores are depleted. This finding is both diagnostic of anemia and an early sign of iron deficiency. Subsequent events are a decrease in serum iron, an increase in serum total iron-binding capacity, and anemia.
During the first half of pregnancy, iron requirements may not be increased significantly, and iron absorbed from food (approximately 1 mg/d) is sufficient to cover the basal loss of 1 mg/d. However, in the second half of pregnancy, iron requirements increase due to expansion of red blood cell mass and rapid growth of the fetus. Increased numbers of red blood cells and a greater hemoglobin mass require approximately 500 mg of iron. The iron needs of the fetus average 300 mg. Thus, the additional amount of iron needed due to the pregnancy is approximately 800 mg. Data published by the Food and Nutrition Board of the National Academy of Sciences show that pregnancy increases a woman’s iron requirements to approximately 3.5 mg/d. This need outstrips the 1 mg/d of iron available from the normal diet.
It is unclear whether the well-nourished, nonanemic woman benefits from routine iron ...