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General dropsy of the foetus is a rare condition in which the foetus and placenta are markedly oedematous. As the result of infiltration with serum the former may attain immense proportions and the latter may be increased to three or four times its normal size. Although a good deal has been written on the subject, no satisfactory explanation of the anomaly has as yet been arrived at.
—J. Whitridge Williams (1903)
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Little was written of fetal disorders in the first edition of this textbook. General dropsy described above is today known as hydrops fetalis (Hydrops Fetalis). Hydrops is perhaps the quintessential fetal disorder, as it can be a manifestation of severe illness from a wide variety of etiologies. Fetal disorders may be acquired—such as alloimmunization, they may be genetic—congenital adrenal hyperplasia or α4-thalassemia, or they may be sporadic developmental abnormalities—like many structural malformations. In this chapter, fetal anemia and thrombocytopenia as well as immune and nonimmune fetal hydrops are reviewed. Fetal structural malformations are reviewed in Chapter 10, genetic abnormalities in Chapters 13 and 14, and conditions amenable to medical and surgical fetal therapies in Chapter 16. Because congenital infections arise as a result of maternal infection or colonization, they are considered in Chapters 64 and 65.
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Of the many causes of fetal anemia, one of the most frequent is red cell alloimmunization, which results from transplacental passage of maternal antibodies that destroy fetal red cells. Alloimmunization leads to overproduction of immature fetal and neonatal red cells—erythroblastosis fetalis—a condition now referred to as hemolytic disease of the fetus and newborn (HDFN).
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In addition, several congenital infections are also associated with fetal anemia, particularly parvovirus B19, discussed in Chapter 64 (Respiratory Viruses). In Southeast Asian populations, α4-thalassemia is a common cause of severe anemia and nonimmune hydrops. Fetomaternal hemorrhage occasionally creates severe fetal anemia and is discussed in Fetomaternal Hemorrhage. Rare causes of anemia include red cell production disorders—such as Blackfan-Diamond anemia and Fanconi anemia; red cell enzymopathies—glucose-6-phosphate dehydrogenase deficiency and pyruvate kinase deficiency; red cell structural abnormalities—hereditary spherocytosis and elliptocytosis; and myeloproliferative disorders—leukemias. Anemia may be identified through fetal blood sampling, described in Chapter 14 (Fetal Blood Sampling), or by Doppler evaluation of the fetal middle cerebral artery (MCA) peak systolic velocity, described in Management of the Alloimmunized Pregnancy.
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Progressive fetal anemia from any cause leads to heart failure, hydrops fetalis, and ultimately death. Fortunately, the prevalence and the course of this otherwise devastating disorder have been dramatically changed by prevention and treatment. Prevention of D alloimmunization is with anti-D immune globulin. Identification and treatment of fetal anemia is with MCA Doppler studies and intrauterine transfusions, respectively. Severely anemic fetuses transfused in utero have survival rates exceeding 90 percent, and even in cases of hydrops fetalis, survival rates approach 80 ...