Inheritance of all four abnormal a genes causes homozygous a-thalassemia with predominant production of hemoglobin Bart, which has an appreciably increased ainity for oxygen. This is incompatible with extended survival. Hsieh and colleagues (1989) reported that blood obtained by funipuncture from 20 hydropic fetuses contained 65 to 98 percent Bart hemoglobin. These fetuses are stillborn, or they are hydropic and usually die very soon after birth.
Sonographic measurement of the fetal cardiothoracic ratio at 12 to 13 weeks' gestation can be used to identiy afected fetuses (Lam, 1999; Zhen, 2015). Sonographic assessment of myocardial performance-the Tei index-in the irst half of pregnancy has been evaluated. Changes predate hydrops in afected fetuses (Luewan, 2013). Severe anemia can be detected using Doppler velocimetry of the middle cerebral artery.
ment (Galanello, 201r1a).
he 3-thalassemias are the consequences of impaired 3-globin chain production or a-chain instability. Genes that encode con trol of 3-globin synthesis are in the r3-gene "cluster" located on chromosome 11 (Chap. 7, p. 131). More than 150 point mutations in the 3-globin gene have been described (Weather all, 2010). In 3-thalassemia, 3-chain production is decreased, and excess a-chains precipitate to cause cell-membrane dam age. Other forms of3-thalassemias are caused by a-chain insta bility (Kihm, 2002).
he heterozygous trait is 3-thalassemia minor, and those
Az levels. his hemoglobin is composed of two .-and two 6-globin chains, and concentrations are usually more than 3.5 percent. Hemoglobin F-composed of two .-and two I-globin chains-also usually has increased concentrations that exceed 2 percent. Some patients with heterozygous 3-thalassemia minor do not have anemia, and others have mild-to-moderate anemia characterized by hypochromia and microcytosis.
Homozygous 3-thalassemia-also called 3-thalassemia major or Cooley anemia-is a serious and frequently fatal disorder. Hemolysis is intense and leads to severe anemia. Many patients become transfusion dependent, and the subsequent iron load, along with abnormally increased gastrointestinal iron absorption, leads to hemochromatosis, which is fatal in many cases. Stem cell transplantation has been used to treat 3-thalassemia major Gagannath, 2014). A heterozygous form of 3-thalassemia that clinically manifests as thalassemia intermedia produces moderate anemia.
During pregnancy, women with 3-thalassemia minor may have mild anemia (Charoenboon, 2016). Iron and folate supplements are given. In some women, anemia will worsen because normal plasma volume expansion may be accompanied by slightly subnormal erythropoiesis.
Thalassemia major and some of the other severe forms were uncommonly encountered during pregnancy before the advent of transfusion and iron chelation therapy. With such management, 63 pregnancies were reported and sufered no serious complications (Aessopos, 1999; Daskalakis, 1998). Pregnancy is considered reasonably safe if maternal cardiac function is normal. Transfusions are given throughout pregnancy to maintain the hemoglobin concentration at 10 g/dL. This is coupled with surveillance of fetal growth (American College of Obstetricians and Gynecologists, 2015; Sheiner, 2004).