Pregnant women are susceptible to hematological abnormalities that may affect any woman of childbearing age. These include chronic disorders such as hereditary anemias, immunological thrombocytopenia, and malignancies such as leukemias and lymphomas. Other disorders arise during pregnancy because of pregnancy-induced demands. Two examples are iron deficiency and megaloblastic anemias. Pregnancy may also unmask underlying hematological disorders such as compensated hemolytic anemias caused by hemoglobinopathies or red cell membrane defects. Finally, any hematological disease may first arise during pregnancy. Importantly, pregnancy induces physiological changes that often confuse the diagnosis of these hematological disorders and assessment of their treatment. Several pregnancy-induced hematological changes are discussed in detail in Chapter 4 (Hematological Changes).
Extensive hematological measurements have been made in healthy nonpregnant women. Concentrations of many cellular elements that are normal during pregnancy are listed in the Appendix (Serum and Blood Constituents). The Centers for Disease Control and Prevention (CDC) (1998) defined anemia in iron-supplemented pregnant women using a cutoff of the 5th percentile—11 g/dL in the first and third trimesters, and 10.5 g/dL in the second trimester (Fig. 56-1). An ongoing study of 278 women is currently evaluating the accuracy of an erythrogram and serum ferritin levels for anemia diagnosis and prediction of responsiveness to oral iron (Bresani, 2013).
The modest fall in hemoglobin levels during pregnancy is caused by a relatively greater expansion of plasma volume compared with the increase in red cell volume (Chap. 4, Hematological Changes). The disproportion between the rates at which plasma and erythrocytes are added to the maternal circulation is greatest during the second trimester. Late in pregnancy, plasma expansion essentially ceases, while hemoglobin mass continues to increase.
The causes of anemia in pregnancy and their frequency are dependent on multiple factors such as geography, ethnicity, nutritional status, preexisting iron status, and prenatal iron supplementation. Other factors are socioeconomic, and anemia is more prevalent among indigent women (American College of Obstetricians and Gynecologists, 2013a). Approximately 25 percent of almost 48,000 Israeli pregnant women had a hemoglobin level < 10 g/dL (Kessous, 2013). Ren and colleagues (2007) found that 22 percent of 88,149 Chinese women were anemic in the first trimester. Of 1000 Indian women, half were anemic at some point, and 40 percent were throughout pregnancy (Kumar, 2013). The importance of prenatal iron therapy is illustrated by the study of Taylor and associates (1982), who reported that hemoglobin levels at term averaged 12.7 g/dL among women who took supplemental iron compared with ...