OUTCOME OF VERY PRETERM BIRTH - CHILDREN REVIEWED WITH EASE AT 2 YEARS DIFFER FROM THOSE FOLLOWED UP WITH DIFFICULTY

Aim-To determine whether those most easily reviewed in a population pr evalence study differ from those followed up only with difficulty. Met hods-All babies born before 32 weeks of gestation in the North of Engl and in 1983, 1990, and 1991 were traced, and all the survivors assesse d at two years by one of two independent clinicians. Results-818 of th e 1138 Live born babies survived to discharge. There was some non-sign ificant, excess disability in the 5% of long term survivors who were d ifficult to trace because of social mobility, but eight times as much severe disability in the 1% (9/796) in care and in the 5% (38/796) who se parents initially failed to keep a series of home or hospital appoi ntments for interview, and five times as much emergent disability in t he 2.7% (22/818) who died after discharge but before their second birt hday. Had the babies who were seen without difficulty been considered representative of all the babies surviving to discharge, the reported disability rate would have been two thirds what it really was (6.9% in stead of 11.0%). Conclusions-Population prevalence studies that ignore those who seem reluctant to cooperate risk serious ascertainment bias .