A new FDA-cleared test using fluorescence in situ hybridization allows the rapid detection of the most common abnormalities of chromosome number. These include trisomies of chromosomes 13, 18 and 21 (Down syndrome) and numerical abnormalities of the X and Y chromosomes (Turner and Klinefelter syndromes, XXX and XYY). These disorders account for about 65% or all abnormalities identified at the time of amniocentesis. The test does not detect complete or partial trisomies of the other autosomes, nor partial trisomies of these specific chromosomes. Structural abnormalities of these chromosomes and the other autosomes also are not detected. 

REASONS FOR REFERRAL

• Pregnancies at risk for trisomies of chromosomes 13, 18 and 21 or sex chromosome abnormalities.

• Pregnancies in which anomalies associated with one of these conditions are identified on ultrasound examination.

• Patients at increased risk for fetal trisomy due to a positive maternal serum screening test.

• Pregnancies in which one of the parents is a known carrier of a relevant chromosome rearrangement.

• Pregnancies at >20 weeks gestation and approaching the legal limit for termination. 

• Pregnancies at >30 weeks with abnormal ultrasound findings

• Patients who want confirmation of previous cytogenetic results on amniocentesis.

RESULTS

• Results are generally available in 24 to 48 hours (M-F). Specimens received on Friday may not be reported until Tuesday noon.

• Results are telephoned to the referring physician by either the laboratory director or by the genetic counselor.

• If the results are abnormal, discussions of management options and genetic counseling should be initiated. However, irreversible therapeutic decisions should not be made until confirmation of the abnormality by a conventional karyotype. 

SPECIMEN REQUIREMENTS

• Specimens of amniotic fluid must have a volume of >18 ml and have no visible blood. 

• A Cytogenetics/Biochemical Requisition Form and Prenatal Diagnosis Information form must accompany each specimen. Please mark Aneuvysion test under FISH tests on the requisition. Contact the Cytogenetics Laboratory for further information.