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Test ID: PAD    
Prenatal Aneuploidy Detection, FISH

Useful For Suggests clinical disorders or settings where the test may be helpful

Ruling out aneuploidy of chromosomes 13, 18, 21, X, and Y in a rapid, cost-efficient manner

Clinical Information Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test

Approximately 1/2 of clinically recognizable spontaneous abortions have a major chromosomal anomaly.


Up to 95% of chromosomal abnormalities diagnosed prenatally involve aneuploidy (gain or loss of whole chromosome) of chromosomes 13, 18, 21, X, and Y.


In liveborn infants, about 8/1,000 have a major chromosome anomaly, of which 6.5/1,000 involve aneuploidy of these 5 chromosomes. Therefore, aneuploidy of chromosomes 13, 18, 21, X, and Y accounts for 81% to 95% of major chromosome anomalies in liveborn infants.


Techniques to detect aneuploidy include standard chromosome analysis and FISH. Standard chromosome analysis from amniotic fluid cells or chorionic villi requires 5 to 9 days for culture, harvest, and analysis. FISH, which uses DNA probes and can be performed on cultured and uncultured cells, can rapidly detect aneuploidy of 13, 18, 21, X, and Y in uncultured amniotic fluid cells or chorionic villi. FISH-based analysis may be helpful in medically urgent evaluations of newborn infants suspected to have aneuploidy of 1 of these chromosomes.

Reference Values Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.

An interpretive report will be provided.

Interpretation Provides information to assist in interpretation of the test results

An interpretive report is provided.

Cautions Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances

This test does not detect aneuploidy of chromosomes other than 13, 18, 21, X, or Y. This test does not detect other chromosomal or structural anomalies.


Low levels of mosaicism involving chromosomes 13, 18, 21, X, or Y may not be detected by this procedure.


There may be interpretation problems in cases of maternal cell contamination.


The use of these probes has been approved by the FDA as a stand-alone test. However, we would strongly recommend that a complete chromosome analysis or a detailed ultrasound be performed in conjunction with this diagnostic procedure. In cases where the FISH analysis is normal, a chromosome analysis allows identification of more complex abnormalities and the less common numeric abnormalities of other chromosomes. In cases where the FISH study is abnormal, chromosome analysis can determine whether the abnormality is due to aneuploidy or a complex structural abnormality. Conventional chromosome analysis allows calculation of a more accurate recurrence risk for the family.

Clinical Reference Provides recommendations for further in-depth reading of a clinical nature

1. Maeda T, Ohno M, Matsunobu A, et al: A cytogenetic survey of 14,835 consecutive liveborns. Jap J Hum Genet 1991;36:117-129

2. Whiteman DAH, Klinger K: Efficiency of rapid in situ hybridization methods for prenatal diagnosis of chromosome abnormalities causing birth defects. Am J Hum Genet 1991;49:A1279

3. Ward BE, Gersen SL, Carelli MP, et al: Rapid prenatal diagnosis of chromosomal aneuploidies by fluorescence in situ hybridization: Clinical experience with 4,500 specimens. Am J Hum Genet 1993;52:854-865

Special Instructions and Forms Describes specimen collection and preparation information, test algorithms, and other information pertinent to test. Also includes pertinent information and consent forms to be used when requesting a particular test