Background

Alloimmune thrombocytopenia is the commonest cause of severe neonatal thrombocytopenia. The pathophysiology and diagnosis of the disorder are described elsewhere (Sections 1.1.3, 1.3.3 and Chapter 12). Most cases are diagnosed after birth, hence the commonly used term neonatal alloimmune thrombocytopenia. However, there may be severe effects on the fetus in utero, and this, as well as the aetiology, may be emphasized through the use of the alternative term, alloimmune thrombocytopenia. In contrast to HDFN, alloimmune thrombocytopenia frequently occurs in first pregnancies.

Considerable progress has been made in laboratory aspects of platelet immunology since alloimmune thrombocytopenia was first recognized in the 1950s, allowing more precise diagnosis of the condition (Section 12.4) There have also been advances in fetal and transfusion medicine resulting in improvements in its management, particularly in the antenatal management of women with a previous history of pregnancies affected by alloimmune thrombocytopenia (Section 14.3). These advances in laboratory diagnosis and antenatal management have drawn attention to the fact that the first affected fetus/neonate in a family is only recognized after bleeding has occurred, and this has raised the question of screening for alloimmune thrombocytopenia.

The purpose of this chapter is to review the epidemiology of alloimmune thrombocytopenia and then to consider the case for antenatal screening against the criteria for screening programmes set by the UK's Department of Health National Screening Committee. Finally, areas where knowledge is still lacking, and where research effort should be directed, will be highlighted.