Discrepancies in cytogenetic results between amniocytes and postnatally obtained blood: trisomy 9 mosaicism.

When amniocentesis reveals a mosaic karyotype and the baby presents with multiple malformations, an analysis of the baby's peripheral blood typically reveals a mosaic karyotype. We present a boy who was prenatally diagnosed by amniocentesis as having trisomy 9 mosaicisim but who had normal G-banding results on postnatal blood karyotyping; the patient also exhibited multiple malformations, including a diaphragmatic hernia, arthrogryposis, undescended testes, and characteristic facies. Because of the discrepancy between the phenotype and karyotype, we repeated the chromosomal studies on multiple occasions.