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Fetomaternal Alloimmune Thrombocytopenia (FMAIT)

(also known as Neonatal Alloimmune Thrombocytopenia or NAIT)

Research questions

  • What is the current incidence of symptomatic FMAIT-affected pregnancies in the UK?
  • How are FMAIT-affected pregnancies managed?
  • What are the prognostic features associated with FMAIT?
  • What are the outcomes of FMAIT-affected pregnancies at birth?


FMAIT is the most common cause of severe neonatal thrombocytopenia in otherwise well term infants[1], and is analogous to the fetal/neonatal anaemia caused by haemolytic disease of the newborn (HDN). The condition results from a fetomaternal incompatibility in platelet alloantigen, most commonly HPA-1a, and can lead to serious bleeding, intracranial haemorrhage and sometimes death of the fetus or infant[2]. Incidence of clinically affected infants is estimated to be 1 in 15,000 births (approximately 50 cases per year in the UK)[2][3]. In contrast to HDN, first pregnancies are often severely affected and the diagnosis is usually made with the birth of a first affected infant. There is therefore a current debate about the utility of screening for the condition. A recent evaluation against the National Screening Committee criteria for appraising a screening programme has identified a number of deficiencies in basic epidemiological information needed to assess the utility of antenatal screening[4]. Three areas are determination of the true incidence of severe haemorrhage associated with FMAIT, the clinical outcome of affected cases and identification of prognostic factors. This study will address these topics.

Additionally, there are considerable controversies in the optimal management of FMAIT-affected pregnancies[4]. 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[5]. This descriptive, population-based study will allow the outcomes following different management strategies to be assessed.

Case Definition

All pregnant women with a previous child affected by fetomaternal alloimmune thrombocytopenia or pregnant women otherwise known to be alloimmunised with a platelet-incompatible fetus.

Study size

The study will run initially for one year. The study will aim to collect data on 50 cases through UKOSS and an additional 200 cases through a parallel survey run through the British Paediatric Surveillance Unit (BPSU).


Wellbeing of Women.

Ethics approval

The study has been approved by the London MREC (study ref 05/MRE02/83).

Download the Data Collection Form (DCF)



  1. ^ Dreyfus M, Kaplan C, Verdy E, et al. Frequency of immune thrombocytopenia in newborns: a prospective study. Immune Thrombocytopenia Working Group. Blood 1997; 89(12):4402-6.
  2. a, b Williamson LM, Hackett G, Rennie J et al. The natural history of fetomaternal alloimmunization to the platelet-specific antigen HPA-1a (PlA1, Zwa) as determined by antenatal screening. Blood 1998; 92(7):2280-7.
  3. ^ Serrarens-Janssen VM, Steegers EA, van den Bos A, et al. Experiences with fetomaternal alloimmune thrombocytopenia in the Netherlands over a 2-year period. Acta Obstet Gynecol Scand 2005; 84(2):203.
  4. a, b Murphy MF, Williamson LM, Urbaniak SJ. Antenatal screening for fetomaternal alloimmune thrombocytopenia: should we be doing it? Vox Sang 2002; 83 Suppl 1:409-16.
  5. ^ Rayment R, Brunskill SJ, Stanworth S, et al. Antenatal interventions for fetomaternal alloimmune thrombocytopenia. Cochrane Database Syst Rev 2005; (1):CD004226.

Updated: Tuesday, 17 January 2023 18:02 (v9)

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