In the later months of pregnancy there is a slight increase in the amount of hemoglobin and red corpuscles and a slight increase in the number of white corpuscles, which become markedly accentuated during the first few days of the puerperium.
—J. Whitridge Williams (1903)
There is virtually nothing from the first edition of Williams’ 1903 textbook that addresses the common anemias of pregnancy. Only pernicious anemia is devoted two paragraphs to say it occasionally appeared in pregnancy. Today, it is well known that 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. 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 (Chap. 4).
Normal values for concentrations of many cellular elements during pregnancy are listed in the Appendix. The Centers for Disease Control and Prevention (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). The modest fall in hemoglobin levels and hematocrit values during pregnancy is caused by a relatively greater expansion of plasma volume compared with the increase in red cell volume. 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 accrue.
Mean hemoglobin concentrations (black line) and 5th and 95th percentiles (blue lines) for healthy pregnant women taking iron supplements. (Data from the Centers for Disease Control and Prevention, 1989.)
The causes of more common anemias encountered in pregnancy are listed in Table 56-1. Their frequency is dependent on multiple factors such as geography, ethnicity, socioeconomic level, nutrition, preexisting iron status, and prenatal iron supplementation (American College of Obstetricians and Gynecologists, 2016a). In the United States, the prevalence of anemia in pregnancy is 3 to 38 percent (Centers for Disease Control and Prevention, 1989). In Latin America and the Caribbean, anemia prevalence ranges from 5 to 45 percent among women of childbearing age (Mujica-Coopman, 2015). Rates are also high in Israel, China, India, South Asia, and Africa (Kessous, 2013; Kumar, 2013, Stevens, 2013). Figure 56-2 highlights the global trends in hemoglobin concentrations and anemia thresholds in pregnant and nonpregnant women.