Fetal and neonatal anemia associated with anti-Jr(a) : a case report showing a poorly hemolytic mechanism.

Although recently published case reports suggest the significance of Jr(a) alloimmunization in the obstetric setting, the involved mechanism still remains unclear. Here we report a case of severe fetal and neonatal anemia associated with anti-Jr(a) alloimmunization, which was successfully managed using Doppler assessment of peak systolic velocity of the fetal middle cerebral artery (MCA-PSV). A Japanese woman with anti-Jr(a) (titer 1024) was referred to our department at 20 weeks' gestation. As fetal MCA-PSV exceeded 1.5 multiple of median, labor was induced and a female neonate of 1998 g was delivered vaginally at 33 weeks and 5 days of gestation. The infant's hematocrit and hemoglobin levels were 25.4% and 82 g/L, respectively, but her total bilirubin level (15 µmol/L; 0.9 mg/dL) and reticulocyte counts (4.5%) were low. During the course, the infant showed no apparent signs of hemolysis. Jr(a) alloimmunization should be recognized as a possible cause of fetal anemia with no direct hemolytic process.