Do we really need a screening test for open spina bifida?

In a recent issue of the Journal were published a series of articles 1–4 and an Opinion 5 regarding possible approaches to early diagnosis of open spina bifida (SB) by way of a screening examination of the fetal brain posterior fossa, specifically the cerebral fourth ventricle, as imaged as an intracranial translucency (IT) between the brain stem and choroid plexus. Each of the studies applied a slightly different imaging approach and varying biometry to the target area, with the aim of flagging up suspected cases or ruling out SB during the late first trimester of pregnancy. The WHO defines certain criteria for screening tests 6 . The disease must be of sufficient prevalence and severity and should have a fixed spectrum of symptoms, the screening method should be simple and acceptable, screening should be accurate, confirmation and followup should be available, the disease should be treatable and screening should show improved outcome and a positive cost/benefit ratio. First and foremost, therefore, a screening test is performed because the definitive diagnostic test is too invasive, too expensive, too difficult technically, or otherwise unacceptable or unavailable to the general population. Screening acts as a ‘sieve’ (hence its name): screen-positive cases are caught in the sieve and are referred for further examination, i.e. either a definitive diagnostic test or more invasive, expensive or technically challenging screening. Clearly, prenatal diagnosis of SB as an entity fulfills the criteria of a target lesion for a screening test.