Despite advances in understanding and management in recent years, fetomaternal alloimmune thrombocytopenia remains a significant cause of severe thrombocytopenia in affected fetuses and newborns. It remains the commonest cause of isolated severe thrombocytopenia in an otherwise healthy newborn and can cause severe bleeding including cerebral haemorrhage with potential for long term neurological damage.
Screening for the condition has not been widely adopted although a number of studies have shown that screening identifies significantly more cases than identified following clinical presentation. In the Norwegian context, screening identified cases at a rate of 7:1 compared with the unscreened population and was modelled to be cost-effective.
In subsequent pregnancies, antenatal management is stratified according to risk based on the previous pregnancy outcome. Antenatal intravenous immunoglobulin and the addition of corticosteroids remain the mainstay of antenatal therapy. Fetal platelet transfusion is increasingly utilised only in extremely high risk cases because of the potential for serious complications including fetal loss or unplanned emergent delivery. Substantial variation exists in the dose, and timing of IVIG and steroid therapy and optimal strategies are not well understood.
Platelet transfusion therapy is the key treatment for severe thrombocytopenia in the affected newborn with both random-donor and HPA selected platelets showing efficacy.
HPA-1a and -5b antibodies remain the cause of NAIT in the majority of Caucasian cases. A number of studies have recently demonstrated that fetal platelet genotype can be determined non-invasively from maternal plasma for the 1a antigen, thus eliminating the need for invasive testing in cases where there is paternal heterozygosity.
Monoclonal and recombinant HPA-1a antibodies have been developed and are being studied in a variety of models. These may one day provide alternative treatment approaches.
The Australian NAIT registry was established in 2009 to obtain consistent national data on NAIT cases. Data from the registry will be presented showing the complexity of diagnosis and management.