Successful treatment of extremely severe fetal anemia due to anti-Jra alloimmunization.

BACKGROUND: Although Jr(a) hemolytic disease of the newborn (HDN) is generally considered to be mild, we encountered a case of anti-Jr(a) alloimmunization hydrops fetalis due to extremely severe fetal anemia that required aggressive intrauterine treatment.

CASE REPORT: A Japanese woman developed hydrops fetalis at the 29th week of gestation. Blood examination was highly positive for anti-Jr(a) antibodies. Cordocentesis demonstrated that the fetus had anti-Jr(a) antibodies and the lowest fetal hemoglobin concentration was 2.3 g/dl. After a total of four intravascular transfusions, fetal hydrops improved and a healthy girl of 2,120 g was delivered at the 35th week of gestation. The initial neonatal hemoglobin concentration at birth was 7.2 g/dl. After two straight transfusions, the infant's anemia did not worsen. Anti-Jr(a) antibodies became negative without developing hyperbilirubinemia.

CONCLUSION: The incidence of Jr(a) negativity can lead to underestimation of the risk of Jr(a) alloimmunization. This case shows that anti-Jr(a) alloimmunization may cause HDN and hydrops fetalis.