Spontaneous rise of fetal platelet counts despite increasing anti-HPA-5b antibodies

Maternal anti-HPA alloantibodies are a rare cause of severe fetal thrombocytopenia. So far there have been no reports on the dynamics of maternal anti-HPA-5 during gestation and its effect on the fetus.

We monitored maternal anti-HPA-5b antibody titers and fetal platelet counts during gestation in a woman with known anti-HPA-5b alloimmunization. The patient was a 32-year-old woman in her third pregnancy. The 1st pregnancy and delivery of a healthy child had been uneventful. At delivery, anti-HPA-5b was detectable in the maternal serum. A 2nd pregnancy ended in early miscarriage.

A steady rise in the alloantibody titer was recorded throughout the 3rd pregnancy. Therefore, cordocentesis was performed at 28 weeks of gestation (platelet count 76 x 10(9)/l). Serial platelet transfusions were administered to the fetus at 28, 32, and 37 weeks of gestation. The platelet counts rose spontaneously thereafter and were 220 x 10(9)/l at delivery, despite an increase in the anti-HPA-5b antibody titer. The child developed normally during the first year of life.

This case illustrates the spontaneous recovery of fetal platelet counts in late pregnancy despite a rise in maternal alloantibody titer.