Investigation of the completeness of case ascertainment by UKOSS using FMAIT as one of the candidate conditions
This study used two different capture-recapture methodologies to assess completeness of ascertainment through UKOSS. Using the candidate disorder of fetomaternal alloimmune thrombocytopenia (FMAIT) Dual-System Estimation (DSE) was used to compare case identification through UKOSS with ascertainment through the British Paediatric Surveillance Unit (BPSU). This was compared with data obtained through the information collected by the National Blood Service to assess data validity.
There were 175 cases of FMAIT identified through the three sources over a period of two years. After capture recapture analysis, 196 cases were estimated to have occurred (95%CI 185-208) in 1,332,642 total births, giving an estimated incidence of 1.3 cases per 10,000 births (95%CI 1.1-1.5).
There were 9 known pregnancy losses/deaths amongst the 175 cases (one miscarriage, 3 terminations, 3 stillbirths and two infant deaths). An additional 20 (14%) infants had an intracranial haemorrhage; disability after one year was reported in 11 infants (9%). Of those cases with an adverse outcome, only 23% had a known family history of FMAIT.
The incidence of clinically detected FMAIT estimated from this national study is less than one sixth of that estimated from prospective screening studies. Almost three quarters of cases with serious clinical problems did not have a known family history of FMAIT, highlighting the importance of appropriate assessment of the case for antenatal screening. This study represents a major contribution to the epidemiology of FMAIT in the UK.