Which antibody is most likely to mediate Hemolytic Disease of the Fetus/Newborn (HDFN) in a susceptible pregnancy?

Anti-Jsa is Most Likely to Mediate Hemolytic Disease of the Fetus/Newborn

Anti-Jsa is the most likely antibody among the listed options to mediate Hemolytic Disease of the Fetus/Newborn (HDFN) in a susceptible pregnancy. 1

Risk Stratification of Antibodies for HDFN

According to the American Society of Hematology guidelines, antibodies can be stratified by their risk of causing clinically significant HDFN:

1. High Risk: Anti-Jsa

   • Part of the Kidd blood group system
   • Can result in clinically significant hemolysis in both transfusion and pregnancy settings 1
   • Requires close monitoring during pregnancy when detected

2. Moderate Risk: Anti-M

   • Only when it has an IgG component that can cross the placenta 1, 2
   • Relatively common but accounts for fewer than 15 reported cases of HDFN in published literature 2

3. Low Risk: Anti-Lua, Anti-P1, Anti-N

   • These antibodies are generally considered to have low risk for causing severe HDFN 1
   • Rarely associated with clinically significant hemolysis in pregnancy

Clinical Implications

When antibodies like Anti-Jsa are identified in a pregnant woman, management should include:

• Serial maternal antibody titers
• Middle cerebral artery Doppler studies to detect fetal anemia
• Preparation for potential interventions including intrauterine transfusions if severe fetal anemia develops 1

Important Context

While the question asks about the listed antibodies, it's worth noting that antibodies in the Rh system (D, C, c, E, e) and Kell system have historically been the most common causes of clinically significant HDFN according to the Society for Maternal-Fetal Medicine guidelines 1. In particular:

• Anti-D is the most common cause of severe HDFN
• Anti-K (Kell) and Anti-c can also cause severe HDFN, with Anti-K causing HDFN in 11.6% of at-risk pregnancies and Anti-c in 8.5% 3

Monitoring Recommendations

When high-risk antibodies like Anti-Jsa are detected:

• Monitor maternal antibody titers throughout pregnancy
• Perform regular middle cerebral artery Doppler studies starting at 16-20 weeks gestation
• Prepare for potential interventions including intrauterine transfusions and exchange transfusions after birth 1

Among the specific antibodies listed in the question (Anti-M, Anti-Jsa, Anti-Lua, Anti-P1, and Anti-N), Anti-Jsa clearly poses the highest risk for causing clinically significant HDFN in a susceptible pregnancy.