MEDSCAPE - The Newborn With a Possible Trisomy: Human Genome and Clinical Diagnosis: The Yin and the Yang, Nov 04, 2011

"Every clinician who deals with newborn babies has been faced with this question: Is this a child with Down syndrome? Less commonly, a child is born with multiple anomalies and the diagnosis of trisomy 18 or 13 is raised. In the past, the test available to the clinician was a karyotype. This test took a week in many cases, causing a great deal of angst for families and delayed decision making.
Fluorescence in situ hybridization (FISH) has been available at many labs for several years. The use of FISH for a specific chromosomal deletion has declined with the emergence of microarray, a test capable of doing 180,000 "FISH" at a time. However, the cost of FISH is far less than for microarray, and it is rapid: 24 hours. For the 3 common trisomies -- 13, 18, and 21 -- an aneuploidy FISH is an inexpensive, rapid test to determine the diagnosis. The FISH for 13, 18, and 21 are incubated with white blood cells and are read in 24 hours. It is easy to count 3 markers for any of the common trisomies. The clinician will have the answer within a day."