Fragile X Syndrome, Fetal Analysis


Fragile X testing

Test Details

Turnaround Time

8 - 14 days

If culture is needed, an additional 14-21 days may be required. Additional culture fee may be applied.


Prenatal diagnosis for pregnancies at risk for fragile X syndrome.

Special Instructions

Labcorp clients with 8 digit client account numbers should call 800-345-4363 and Labcorp Genetics & Women's Health clients with 6 digit client /subclient account numbers should call 800-255-7357 to speak with a laboratory genetic coordinator before collecting specimens. In some circumstances, specimens from both parents and other family members may be required. All fetal specimens, including cordblood, must be accompanied by a maternal blood, PurFlock buccal swab kit or Oragene Dx 500 saliva kit for maternal cell contamination (MCC). A separate requisition should be submitted with the maternal specimen.

Test Includes

This test includes the following gene: FMR1


Technologies used do not detect germline mosaicism and do not rule out the presence of large chromosomal aberrations including rearrangements and gene fusions, or variants in regions or genes not included in this test, or possible inter/intragenic interactions between variants, or repeat expansions. Variant classification and/or interpretation may change over time if more information becomes available. False positive or false negative results may occur for reasons that include: rare genetic variants, sex chromosome abnormalities, pseudogene interference, blood transfusions, bone marrow transplantation, somatic or tissue-specific mosaicism, mislabeled samples, or erroneous representation of family relationships. This test was developed and its performance characteristics determined by Labcorp. It has not been cleared or approved by the Food and Drug Administration.


Fragile X syndrome: Polymerase chain reaction (PCR) followed by capillary electrophoresis, and methylation PCR analysis.

Maternal cell contamination analysis (MCC): Analysis of short tandem repeat markers by multiplex fluorescent polymerase chain reaction (PCR) and capillary electrophoresis.


Hunter JE, Berry-Kravis H, et al., FMR1 Disorders. 1998 Jun16 (Updated 2019 Nov 21). In: Adam MP, Ardinger HH, Pagon RA, et al., editors. GeneReviews®[Internet]. PMID: 20301558

Spector E, Behlmann A, Kronquist K, et al. Laboratory testing for fragile X, 2021 revision: a technical standard of the American College of Medical Genetics and Genomics (ACMG). Genet Med 23, 799 (2021). PMID: 33795824

Nagan, M, Faulkner NE, Curtis C, et al. Laboratory Guidelines for Detection, Interpretation, and Reporting of Maternal Cell Contamination in Prenatal Analyses. J Mol Diagn 13, 7 (2011). PMID: 21227389

Specimen Requirements

Information on collection, storage, and volume


Amniotic fluid or chorionic villus sample (CVS) or cultured cells or cordblood. Direct amniotic fluid or CVS specimen may be submitted; additional culture fee may be applied.


Amniotic fluid: 10 mL or CVS: 10 mg or amniotic fluid and CVS culture: two confluent T-25 flasks or 4 mL cordblood. If amniotic fluid or CVS are cultured at another facility, please maintain back-up cultures.

Minimum Volume

Amniotic fluid: 10 mL or CVS: 10 mg or amniotic fluid and CVS culture: two confluent T-25 flasks or 3 mL cordblood


Amniotic fluid or CVS: Sterile plastic conical tube or T-25 flask.
Cordblood: Yellow-top (ACD-A) or lavendar-top (EDTA) tubes

Storage Instructions

Maintain specimen at room temperature. Do not freeze.

Causes for Rejection

Frozen or hemolyzed specimen; quantity not sufficient for analysis; improper container


Standard sterile techniques. Transfer aseptically to sterile tubes. Amniotic fluid: Discard first 2 mL of fluid aspirated to avoid maternal cell contamination.