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INTRODUCTION

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Hemoglobinopathies are inherited disorders that result in abnormal hemoglobin. Broadly speaking, the disorders can be classified as disorders of the quantity of hemoglobin such as thalassemia or structural disorders such as sickle cell anemia. Hemoglobinopathies are relatively common and affect about 5% to 7% of the world’s popu­lation. Sickle cell anemia is the most common monogenic disease. The prevalence of hemoglobinopathies is increasing as more affected children survive to adulthood and subsequently pass on the genotype. Approximately 300,000 children are born worldwide every year who are affected with sickle cell anemia. The prevalence of disease is high in Africa, particularly the sub-Sahara, but also in areas in the Mediterranean, Middle East, and India. Sickle cell trait occurs in about 1 in 8 African Americans and about 1 in 600 African Americans have sickle cell anemia. A variant of sickle cell anemia, sickle-thalassemia (HbSC) is seen in Middle Easterners. It is generally milder than sickle cell anemia but may present for the time in pregnancy which is why it is important to obtain a hemoglobin electrophoresis in the evaluation of anemia in pregnancy.

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Sickle cell anemia is a multisystem disease. (Fig. 28-1) Pregnancies complicated by sickle cell anemia are marked by an increase in maternal and fetal complications. The maternal complications relate to the effects of the multi­organ involvement, chronic hemolysis, increased susceptibility to infection and thrombosis, intermittent crises, increased rates of hypertensive disorders, narcotic dependence, increased potential for sensitization to red cell antigens, hemorrhage, and operative delivery. The fetal effects include increased rates of intrauterine growth restriction, low birth weight, prematurity, and the genetic implications of being either a heterozygote or a homo­zygote for the sickle cell gene.

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FIGURE 28-1

Manifestations of sickle cell disease. (Adapted with permission from Piel F, Stenberg M, Rees D. Sickle cell disease. N Engl J Med. 2017;376(16):1561-1573.)

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PATHOPHYSIOLOGY

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Hemoglobin is the iron-containing transport protein responsible for oxygen delivery from the lungs to the cells. Adults normal have about 95% of their hemoglobin in the form of hemoglobin A1 which consists of two α and two β chains. In addition, there is a small amount of hemoglobin A2 which consists of two α and two δ chains. The predominate fetal hemoglobin has two α and two ϒ chains. As pregnancy progresses, the fetus converts more fetal hemoglobin to adult hemoglobin, a process that continues after birth. Fetal hemoglobin has been reported to increase in pregnancy to as much as 4% of maternal hemoglobin.

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In sickle cell anemia, there is a point mutation in the chain in which valine is substituted for glutamic acid. This results in the formation of hemoglobin S which distorts the normal red cell architecture such that the normal shape and deformability are lost. The crescent shaped cells have diminished capacity for oxygen transport ...

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