At least 90 percent of cases of hydrops are nonimmune (Bellini, 2012; Santolaya, 1992). The prevalence estimate is 1 per 1500 second-trimester pregnancies (Heinonen, 2000). The number of specific disorders that can lead to nonimmune hydrops is extensive. Etiologies and the proportion of births within each hydrops category from a review of more than 6700 afected pregnancies are summarized in Table 1i5-4. A cause is identified in at least 60 percent prenatally and in more than 80 percent postnatally (Bellini, 2009; Santo, 2011). Currently, approximately 20 percent of cases remain idiopathic (Bellini, 2015). As shown in Figure 15-5, several diferent pathophysiological processes are proposed to account for the inal common pathway of hydrops fetalis.
Importantly, the etiology of non immune hydrops varies according to when in gestation it is identified. Of those diagnosed prenatally, aneuploidy accounts for approximately 20 percent, cardiovascular abnormalities for 15 percent, and infections for 14 percent-the most common of these being parvovirus B19 (Santo, 2011). Overall, only 40 percent of pregnancies with nonimmune hydrops result in a liveborn neonate, and of these, the neonatal survival rate is only about 50 percent. Sohan and colleagues (2001) reviewed 87 pregnancies with hydrops and found that 45 percent of those diagnosed before 24 weeks' gestation had a chromosomal abnormality. The most frequent aneuploidy was 45,X-Turner syndrome, and in such cases, the survival rate was <5 percent (Chap. 13, p. 259). If hydrops is detected in the irst trimester, the aneuploidy risk is nearly 50 percent, and most have cystic hygromas (Fig. 10-22, p. 198).
Although the prognosis of nonimmune hydrops is guarded, it is heavily dependent on etiology. In large series from Thailand and Southern China, aA-thalassemia is the predominant cause of nonimmune hydrops, accounting for 30 to 50 percent of cases and conferring an extremely poor prognosis (Liao, 2007; Ratanasiri, 2009; Suwanrath-Kengpol, 2005). In contrast, treatable etiologies such as parvovirus, chylothorax, and tachyarrhythmias, which each comprise about 10 percent of
Anemia Red cell alloimmunization Fetomaternal hemorrhage Hematological disorder Infection Selected fetal anomalies Placental abnormality Volume overload or Extramedullary hematopoiesis Impaired venous return Hepatic dysfunction, Metabolic disorders impaired protein synthesis Infection Tissue hypoxia ? Heart failure Increased hydrostatic pressure Lymphatic abnormality Decreased plasma oncotic pressure Increased capillary permeability Decreased lymphatic flow Increased interstitial fluid Hydrops fetalis
FIGURE 15�5 Proposed pathogenesis of immune and nonimmune hydrops fetalis. (Adapted from Bellini, 2009; Lockwood, 2009.) cases, can result in survival in two thirds of cases with fetal therapy (Sohan, 2001).
Hydrops is readily detected sonographically. As noted, two efusions or one efusion plus anasarca are required for diagnosis. Edema may be particularly prominent around the scalp, or equally obvious around the trunk and extremities. Efusions are visible as luid outlining the lungs, heart, or abdominal viscera (Fig. 15-6).