Rare non‐mosaic trisomies in chorionic villus tissue not confirmed at amniocentesis

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Abstract
This paper reports eight cases of non‐mosaic, rare, and typically lethal trisomies diagnosed in chorionic villi and not confirmed by amniocentesis. Four cases were 47,XX, + 16; two cases were 47,XX, +2; one was 47,XX, + 12; and one was 47,XY, +7. There have been no known complications in any of these gestations. These eight cases were found in a series of approximately 12 000 samples processed in our laboratory (0.07 per cent). We conclude that (1) rare non‐mosaic trisomy not reflecting the fetal condition is an occasional source of diagnostic ambiguity in chorionic villus sampling; and (2) when encountered, a follow‐up amniocentesis should be recommended to the patient to confirm or rule out the abnormality. We propose the term ‘confined placental abnormality’ to describe non‐mosaic trisomies and other related abnormalities found only in chorionic tissue.