Hemolytic Disease of the Fetus and Newborn

Hemolytic disease of the fetus and newborn (HDFN), historically called erythroblastosis fetalis, is the destruction of fetal or neonatal red cells by maternal IgG alloantibodies that cross the placenta. It classically results from maternal anti-D when an RhD-negative mother is sensitized to RhD-positive fetal red cells, but other red-cell antibodies, including those of the ABO system, can also cause it. The condition ranges from mild anemia and jaundice to severe fetal anemia with hydrops.

Definition

Hemolytic disease of the fetus and newborn is alloimmune hemolysis in which maternal IgG antibodies against fetal red-cell antigens cross the placenta and destroy fetal or neonatal red cells, most classically due to RhD incompatibility.

Scope

This entry covers the immune basis of HDFN — maternal alloimmunization and transplacental transfer of IgG antibody — the antibodies most often responsible (notably anti-D and ABO antibodies), the spectrum from mild jaundice to hydrops fetalis, and the principle of preventing RhD sensitization with anti-D immunoglobulin. It is a reference topic and not a management protocol.

Core questions

• How does maternal alloimmunization lead to fetal red-cell destruction?
• Why is anti-D the classic cause of severe HDFN?
• How does ABO HDFN differ from Rh HDFN in severity?
• On what principle does anti-D immunoglobulin prevent RhD sensitization?

Key concepts

• Maternal alloimmunization
• Transplacental IgG transfer
• RhD incompatibility and anti-D
• ABO HDFN
• Hydrops fetalis
• Neonatal jaundice and hyperbilirubinemia
• Anti-D (Rh) immunoprophylaxis

Mechanisms

When fetal red cells carrying a paternally inherited antigen that the mother lacks enter the maternal circulation, the mother may form IgG alloantibodies. Because IgG crosses the placenta, these antibodies can bind fetal red cells in a subsequent (or the same) pregnancy and cause extravascular hemolysis, producing fetal anemia and, after birth, hyperbilirubinemia as the neonate clears antibody-coated cells. Severe anemia can lead to high-output failure and hydrops fetalis. RhD is the most immunogenic antigen and the classic cause; ABO HDFN tends to be milder because the antibodies and antigen expression differ. The antiglobulin test detects maternal antibody and antibody coating fetal/neonatal cells, and the recognition that RhD sensitization could be prevented led to anti-D immunoglobulin prophylaxis.

Clinical relevance

HDFN is a central example of how blood-group alloimmunization causes disease across the placenta, and its prevention through anti-D immunoprophylaxis is one of the major successes of immunohematology. This entry explains the underlying immunology and the principle of prevention; it does not give dosing or individualized obstetric or neonatal management advice.

Epidemiology

Severe Rh HDFN has become much less common in settings with routine anti-D immunoprophylaxis, which markedly reduced RhD alloimmunization. ABO incompatibility is a more frequent but generally milder cause of neonatal hemolysis, and HDFN from other red-cell antibodies persists, so antenatal antibody screening remains important.

History

Levine and Stetson in the late 1930s and Landsteiner and Wiener in the 1940s linked the condition to Rh incompatibility, explaining erythroblastosis fetalis as maternal sensitization to fetal red cells. The antiglobulin test of Coombs, Mourant and Race (1945) allowed detection of the responsible antibodies, and the development of anti-D immunoglobulin in the 1960s, evaluated in trials later summarized in systematic reviews, made prevention of RhD sensitization possible.

Key figures

• Philip Levine
• Karl Landsteiner
• Cyril Clarke
• Ronald Finn
• Robin Coombs

Seminal works

• coombs-1945
• crowther-2013
• avent-2000

Frequently asked questions

Why does Rh hemolytic disease usually spare the first pregnancy?

Sensitization typically occurs when fetal RhD-positive cells enter the maternal circulation, often around delivery, so the resulting maternal anti-D more commonly affects a subsequent RhD-positive pregnancy.

Is ABO hemolytic disease of the newborn usually severe?

ABO HDFN is generally milder than Rh disease and often causes neonatal jaundice rather than severe fetal anemia, though it is more common because ABO incompatibility between mother and fetus is frequent.