Low-level mosaicism for both trisomy 15 and monosomy-X in amniotic fluid cells confirmed in fetal tissues

Prenatally detected true double trisomy mosaic 12 and 13 not confirmed in fetal and placental tissues by conventional cytogenetic methods, but suggested by FISH analysis

“…The clinical signi®cance of true mosaicism in routine cytogenetic diagnosis continues to be dif®cult to interpret because the origin of the aberrant cell line is not known and the fetal phenotype can not be accurately predicted (Hansson et al, 1998;Wilson et al, 1989). A clear distinction between aberrations of true fetal origin, con®ned to extra fetal origin, or of aberrations due to in vitro artefacts is essential for predicting the clinical outcome (Welborn and Lewis, 1990;Djalali et al, 1991).…”