Hemolytic disease of the fetus/newborn due to Jr(a) immunization is very rare and considered to be mild, and only routine obstetrical care is recommended for pregnant women sensitized to the Jr(a) antigen.
A 20-year-old nulliparous woman was referred to our hospital for perinatal management. Her indirect Coombs test was positive for anti-Jr(a) antibody (1:64). At 33 weeks' gestational age, we observed that fetal growth was mildly restricted and the peak systolic velocity of the fetal middle cerebral artery (PSV-MCA) was above the upper limit of the reference range (1.55 multiples of the median). Amniocentesis was also carried out and the DeltaOD450 value was in the lower mid-zone of the Liley curve. We continued to carefully observe the patient because we observed PSV-MCA values within 1.50-1.60 multiples of the median and no other findings of fetal anemia. She vaginally delivered a female infant weighing 2,136 g at 37 weeks' gestational age. The infant received treatment with both iron and recombinant erythropoietin without developing hyperbilirubinemia and blood transfusion.
PSV-MCA should be monitored for the detection of fetal anemia, even in pregnant women sensitized to some antigens for which only routine obstetrical care is recommended.
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