Discordant direct and culture results following chorionic villus sampling and the diagnosis of a third cell line in the fetus

We report a case of discordant non-mosaic karyotypes following chorionic villus sampling (CVS). A 45,XX,der(21;21)(q10;q10) karyotype was found on direct preparation of cytotrophoblasts and 46,XX was found on long-term culture of mesenchymal core cells. Analysis of amniotic fluid cells and fetal tissue revealed a third karyotype: 46,XX,+21,der(21;21)(q10;q10). Had only culture analysis been performed, follow-up studies might not have been undertaken. This case demonstrates the importance of direct CVS preparation in helping to identify fetal abnormalities, and the need for follow-up of discordant CVS results.