VI. PROGNOSIS/CLINICAL COURSE

The blood bank reports the presence of an anti-Fy^a antibody. Antibodies against Fy^a occur in 0.8/1000 samples from pregnant women. Among susceptible infants, the distribution of the severity of HDN due to anti-Fy^a antibodies is as follows:

• 94% none or mild HDN
• 2% moderate HDN
• 4% severe HDN

HDN is a transient disease, because maternal antibody titers decline with time in the infant’s circulation. What is the approximate half-life of the maternal IgG anti-Fy^a antibody in this child’s circulation?