Pregnant women are susceptible to several hematological abnormalities that may affect any woman of childbearing age. These include chronic disorders such as hereditary anemias, immunological thrombocytopenia, and hematological malignancies. Other disorders arise from pregnancy-induced demands. Two are iron deficiency and megaloblastic anemias. Pregnancy may also unmask underlying hematological conditions. Importantly, pregnancy induces physiological changes that often confuse diagnosis and assessment of these disorders (Chap. 4, p. 60).
Normal values for concentrations of many cellular elements during pregnancy are listed in the Appendix (p. 1227). The Centers for Disease Control and Prevention (1998) defined anemia in iron-supplemented pregnant women using a cutoff of the 5th percentile, which is 11 g/dL in the first and third trimesters and 10.5 g/dL in the second trimester. Notably, these were not based on a U.S. population. Table 59-1 describes the distribution of hematocrit values of 480 iron-sufficient women at Parkland Hospital (Zofkie, 2020). Using these data, values below 30 percent seem reasonable to define anemia.
TABLE 59-1Hematocrit Values in Pregnancy ||Download (.pdf) TABLE 59-1Hematocrit Values in Pregnancy
| ||Percent |
| ||5th percentile ||50th percentile ||75th percentile |
|1st trimester ||33.0 ||37.5 ||41.2 |
|2nd trimester ||30.5 ||35.7 ||39.2 |
|Predelivery ||30.7 ||36.5 ||40.5 |
The modest fall in hemoglobin and hematocrit values during pregnancy stems from a relatively greater expansion of plasma volume compared with red cell volume (Georgieff, 2020). The disproportion between the rates at which plasma and erythrocytes add to the maternal circulation is greatest during the second trimester. Late in pregnancy, plasma expansion essentially ceases, while hemoglobin mass continues to accrue.
The causes of more common anemias encountered in pregnancy are listed in Table 59-2. 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, 2021). In the United States, the prevalence of anemia in pregnancy is 3 to 38 percent (Centers for Disease Control and Prevention, 1989).
TABLE 59-2Causes of Anemia During Pregnancy ||Download (.pdf) TABLE 59-2Causes of Anemia During Pregnancy
| Iron-deficiency anemia |
| Acute blood-loss anemia |
| Anemia of chronic disease |
| Megaloblastic anemia |
| Hemolytic anemias |
| Aplastic or hypoplastic anemia |
| Thalassemias |
| Sickle-cell hemoglobinopathies |
| Other hemoglobinopathies |
| Hemolytic anemias |
Initial evaluation of a pregnant woman with moderate anemia includes measurements of hemoglobin, hematocrit, red cell indices, and serum iron or ferritin levels; careful examination of a peripheral blood smear; and a sickle-cell preparation if the woman has African lineage (Appendix p. 1227).
Effects on Pregnancy Outcomes
Anemia is associated with several adverse pregnancy outcomes (American College of Obstetricians and Gynecologists, 2021; Rahmati, 2020). Most anemia studies during ...