Down's syndrome screening: a controversial test, with more controversy to come!

Recently, Professor Reynolds eloquently highlighted some of the current controversies surrounding the provision of Down's syndrome screening, primarily from a biochemical standpoint,¹ and most of those involved in this field would certainly agree with the last part of the title. Nevertheless, there are several issues raised in the article, which require some further clarification to achieve a balanced discussion. First, the issue of intrauterine lethality and detection of affected fetuses that may spontaneously abort is one that potentially affects all forms of prenatal diagnosis and screening, not just ultrasound screening for nuchal translucency thickness (NT), as implied. Second, this issue only becomes important, in terms of evaluating detection rates, if those fetuses that are destined to abort spontaneously are preferentially detected by the screening test. In a study on this issue using data from individual pregnancies, rather than epidemiological models, …