Prenatal testing for hemolytic disease of the newborn and fetal neonatal alloimmune thrombocytopenia - current status.

Incompatibility of red cell and platelet antigens can lead to maternal alloimmunization causing hemolytic disease of the fetus & newborn and fetal neonatal alloimmune thrombocytopenia respectively. As the molecular background of these polymorphisms emerged, prenatal testing using initially fetal DNA obtained from invasively obtained amniotic fluid or chorionic villus was implemented. This evolved into testing using maternal plasma as source of fetal DNA, and this is in routine use as a safe non-invasive diagnostic that has no risk to the fetus of alloimmunization or spontaneous miscarriage. These tests were initially applied to high risk pregnancies, but has been applied on a mass scale, to screen fetuses in D-negative pregnant populations as national screening programs. Fetal neonatal alloimmune thrombocytopenia management has had comparatively small take up in non-invasive testing for causative fetal platelet alleles (e.g., HPA-1A), but mass scale genotyping of mothers to identify at risk HPA-1b1b pregnancies and their treatment with prophylactic anti-HPA-1A is being considered in at least one country (Norway).