Prenatal confirmation of true fetal trisomy 22 mosaicism by fetal skin biopsy following normal fetal blood sampling

Trisomy 22 mosaicism diagnosed at 20 weeks' gestation by amniocentesis in a 35-year-old woman was not confirmed by fetal blood sampling. Subsequent fetal skin biopsy revealed trisomy 22 in 7 of the 15 fibroblasts analysed. We conclude that, depending on the chromosome involved, fetal skin biopsy should be considered in the diagnostic work-up when mosaicism is found in amniotic fluid.