Prenatal diagnosis/Authors' reply

[Allan Caine] and colleagues' conclusion from the analysis of their karyotype data is that "substantial numbers of liveborn children with hitherto preventable mental or physical handicaps" will be born if full karyotype analysis is no longer done on prenatal samples from women referred for increased risk of Down's syndrome, in line with recent UK National Screening Committee (UKNSC) recommendations. We believe this conclusion to be exaggerated by the inclusion of a socalled "low to high risk" karyotype group in their final calculations of the number of babies likely to be born with congenital abnormalities. These karyotypes include de novo balanced rearrangements, which have a quoted risk of only 6% of phenotypic abnormality (3% above the background general population risk of abnormal phenotype); small marker chromosomes, many of which are benign; and trisomies undetected by rapid testing, many of which will miscarry before reaching term; this group might therefore be better defined as being of "unknown or unpredictable prognosis".