Normal pregnancy is characterized by an increase in maternal plasma volume of about 50% and an increase in red cell volume of about 25%. Because of these changes, the mean hemoglobin and hematocrit values are lower than in the nonpregnant state. Anemia in pregnancy is considered when the hemoglobin measurement is below 11 g/dL. By far, the most common causes are iron deficiency and acute blood loss anemia, the latter usually occurring in the peripartum period. Symptoms such as fatigue and dyspnea that would otherwise suggest the presence of anemia in nonpregnant women are common in pregnant women; therefore, periodic measurement of hematocrits in pregnancy is essential so that anemia can be identified and treated. In addition to its impact on maternal health, untoward pregnancy outcomes such as low birthweight and preterm delivery have been associated with second- and third-trimester anemia.
A. Iron Deficiency Anemia
The increased requirement for iron over the course of pregnancy is appreciable in order to support fetal growth and expansion of maternal blood volume. Dietary intake of iron is generally insufficient to meet this demand, and it is recommended that all pregnant women receive about 30 mg of elemental iron per day in the second and third trimesters. Oral iron therapy is commonly associated with gastrointestinal side effects, such as nausea and constipation, and these symptoms often contribute to noncompliance. If supplementation is inadequate, however, anemia often becomes evident by the third trimester of pregnancy. Because iron deficiency is by far the most common cause of anemia in pregnancy, treatment is usually empiric and consists of 60–100 mg of elemental iron per day and a diet containing iron-rich foods. Iron studies can confirm the diagnosis if necessary (see Chapter 13-01), and further evaluation should be considered in patients who do not respond to oral iron. Intermittent iron supplementation (eg, every other day) has been associated with fewer side effects and may be reasonable for women who cannot tolerate daily therapy.
B. Folic Acid Deficiency Anemia
Megaloblastic anemia in pregnancy is almost always caused by folic acid deficiency, since vitamin B12 deficiency is extremely uncommon in the childbearing years. Folate deficiency is usually caused by inadequate dietary intake of fresh leafy vegetables, legumes, and animal proteins. The daily requirement of folic acid increases in pregnancy, and supplementation with 0.4 mg of folate is recommended. Importantly, this dose taken during the periconceptional period has also been shown to reduce the risk of neural tube defects in the offspring. Multiple gestation, infections, malabsorption, and use of anticonvulsant drugs such as phenytoin can precipitate folic acid deficiency, and additional folate supplementation should be considered in these settings. Lactating women continue to have an increased demand for folate, and the diagnosis is sometimes made in the puerperium.
The diagnosis is made by finding macrocytic red cells and hypersegmented neutrophils on a blood smear (see Chapter 13-06...