The clinical presentation and ultrasound is consistent with hydrops fetalis, an example of a type II hypersensitivity reaction, in which antibodies bind to antigens on a cell's surface leading to phagocytosis or lysis. Note the presence of edema in the ultrasound image.
In hydrops fetalis, an Rh- pregnant woman who has previously been exposed to the Rh antigen mounts an immune response when exposed to fetal Rh antigen. This response leads to the production of IgM and IgG. IgG crosses the placenta into fetal circulation, binding fetal RBCs, targeting them for destruction. This accounts for the fetal anemia and increased unconjugated bilirubin.
Jardine et al. state that nonphysiologic causes of newborn jaundice include blood group incompatibility (rhesus or ABO problems), other causes of hemolysis, sepsis, bruising, and metabolic disorders. They emphasize that in newborns, unconjugated bilirubin can penetrate the blood-brain barrier and is potentially neurotoxic.
Fung et al. discuss the guidelines on use of anti-D prophylaxis to optimize prevention of rhesus (Rh) alloimmunization. They found that there is a decreased incidence of Rh alloimmunization when immunoprophylaxis strategies are applied.
Illustration A depicts antibody-mediated opsonization. Note how the antibody serves to bring the pathogen and phagocyte into close association; this helps facilitate phagocytosis.
Illustration B summarizes the pathophysiology of Rh incompatibility.
Answer 1: Anaphylaxis would be more consistent with a type I hypersensitivity reaction.
Answer 3: The main route of RBC lysis in fetal hydrops is via antibody-mediated opsonization, not cytotoxic T cells.
Answer 4: Type III hypersensitivity reactions involve the deposition of immune complexes, not antibody-mediated opsonization.
Answer 5: Type IV hypersensitivity reactions are delayed-type and are mediated by T-cells, not NK cells.
Jardine LA, Woodgate P. Neonatal jaundice. Am Fam Physician. 2012 Apr 15;85(8)
PMID:22534393 (Link to Abstract)
Fung Kee Fung K, Eason E, Crane J, Armson A, De La Ronde S, Farine D, Keenan-Lindsay L, Leduc L, Reid GJ, Aerde JV, Wilson RD, Davies G, Désilets VA, Summers A, Wyatt P, Young DC; Maternal-Fetal Medicine Committee, Genetics Committee. Prevention of Rh alloimmunization. J Obstet Gynaecol Can. 2003 Sep;25(9)
PMID:12970812 (Link to Abstract)