mosaic abnormality

The clinical effect of a mosaic abnormality detected
prenatally is difficult to predict. Most cases of mosaicism for
chromosome 20 detected at amniocentesis, for example, are
not associated with fetal abnormality. The trisomic cell line is
often confined to extra fetal tissues, with neonatal blood and
fibroblast cultures revealing normal karyotypes in infants
subsequently delivered at term. In some cases, however, a
trisomic cell line is detected in the infant after birth and this
may be associated with physical abnormalities or developmental
delay.