Surveillance of fetomaternal alloimmune thrombocytopenia

Summary

Feto Maternal Alloimmune thrombocytopenia (FMAIT), also known as neonatal alloimmune thrombocytopenia (NAIT) is the most common cause of severe neonatal thrombocytopenia in otherwise well term infants, and can lead to serious bleeding, intracranial haemorrhage and sometimes death of the fetus or infant. First pregnancies are often severely affected and the diagnosis is usually made with the birth of a first affected infant. There is a current debate about the utility of antenatal screening for the condition. Additionally, there are considerable controversies in the optimal management of FMAIT-affected pregnancies. There is no clear approach to the antenatal management of first affected pregnancies, and several questions remain in the approaches to managing second and subsequent affected pregnancies. This descriptive, population-based study addressed deficiencies in basic epidemiological information about the condition highlighted in a recent evaluation against National Screening Committee criteria for appraising a screening programme.

Key findings

• This study identified cases between October 2006 and September 2008 through UKOSS, the British Paediatric Surveillance Unit (BPSU) and the NHS Blood and Transplant Platelet Immunology database, and followed affected infants to one year of age.
• The estimated incidence of clinically detected FMAIT was 12.4 cases per 100,000 total births (95%CI 10.7-14.3).
• Fifty-two cases (30%) were known at the start of pregnancy; 120 (70%) were unknown (n=115) or unrecognised (n=5).
• Cases known at the outset of pregnancy were more likely to be delivered by caesarean section (82% vs 30%, p<0.001), had higher platelet counts at birth and were less likely to have a platelet count below 20 x 10⁹/l at birth than cases not known at pregnancy outset (2% vs 58%, p<0.001).
• Unknown cases were more likely to experience any hemorrhagic complication (67% vs 5%) (p<0.001) and more likely to have an intracranial haemorrhage (20% vs 4%) (p=0.014) than known cases receiving antenatal management.
• In view of the incidence of severe disease identified, further assessment of the case for antenatal screening is important. There were a number of cases in which the significance of a history of FMAIT in a previous sibling was not recognised and there is a need for continuing awareness of the importance of this diagnosis.

Publications

Journal Articles

• Knight M, Pierce M, Allen D, Kurinczuk JJ, Spark P, Roberts DJ, Murphy MF. The incidence and outcomes of fetomaternal alloimmune thrombocytopenia: a UK national study using three data sources. Br J Haematol. 2011;152(4):460-8.