Screening for fetal and neonatal alloimmune thrombocytopenia: is it possible and what are the potential outcomes?

Abstract

Fetal and neonatal alloimmune thrombocytopenia (FNAIT) is a rare but potentially very serious bleeding condition affecting the fetus/newborn. The vast majority (>80%) of FNAIT cases among Caucasians, and the most serious one, are caused by maternal antibodies to the human platelet antigen 1a (HPA‐1a). The clinical consequences of FNAIT span a continuum from no symptoms to intracranial haemorrhage (ICH) and intrauterine death. The incidence of FNAIT‐associated ICH has been estimated to be around 1 in 10 000 newborns. For many reasons, FNAIT has not been considered for prophylactic efforts similar to those that have been used for the prevention of HDFN, caused by antibodies against RhD: first, HPA‐1a typing kits are not well suited to the workflow in immunohaematology laboratories; secondly, the costs associated with HPA‐1a typing of all pregnant women have been a hindrance; thirdly, there is no international consensus regarding the optimal antenatal management of HPA‐1a‐immunized women identified in a screening programme; fourthly, it has generally been believed that immunization against HPA‐1a mostly takes place during the first incompatible pregnancy, and finally, there is yet no medicinal product available that can prevent HPA‐1a‐immunization in the same way as anti‐D can prevent RhD immunization. Implementation of HPA‐1a typing of all pregnant women has been discussed by the health authorities in several European countries. The abovementioned five hindrances for FNAIT screening and the Wilson and Jungner criteria for screening programmes will be discussed in the light of recent advances within FNAIT research.

New elegant methods for maternal and fetal HPA‐1a typing

“…Furthermore, those very few HLA‐DRB3*01:01 negative women who become HPA‐1a immunized will only produce very low levels of anti HPA‐1a, and the vast majority of these women will give birth to a child with a normal platelet count, or, occasionally, to a child with only moderate thrombocytopenia, with no or little clinical consequence . Hence, close clinical follow‐up during pregnancy of HPA‐1a negative/HLA‐DRB3*01:01 negative women is not necessary, neither is treatment with IVIG if they should become HPA‐1a immunized …”