Fetal Cells in Maternal Blood: A Six-Fold Increase in Women who have Undergone Amniocentesis and Carry a Fetus with Down Syndrome: A Multicenter Study - Falcidia, E; Parano, E; Grillo, A; Pavone, P; Takabayashi, H; Trifiletti, R R; Scollo, P; Dallapiccola, B; Grammatico, P; Novelli, A; Paladini, D; Monni, G; Gulisano, A; Scassellati, G (Neuropediatrics, 2004)