Prenatal and Fetal Genetic Testing

Clinical Indications

• Increased Risk for aneuploidy based on maternal serum testing or Non-invasive prenatal screening (NIPS)
• Fetal abnormalities found on ultrasound
• Intrauterine Fetal Demise
• Family History of a specific genetic condition

Sample Requirements

Amniotic Fluid: 15-30mL amniotic fluid in sterile 15mL culture tube. Do not centrifuge or freeze. Ship at room temperature within 24 hours.

CVS: 25-50mg in sterile culture media. Do not freeze. Ship at room temperature within 24 hours.

NIPT (by Medical Genetics or MFM referral only): Peripheral blood- 10ml cell free streck tube, tube must be full. Do not centrifuge or freeze. (IWK meditech: NIPT)

Fetal Tissue (POC/fetal demise): If dry ice is available, freeze at -80˚C upon collection (with no added saline) and send on dry ice. If dry ice is not available, do not freeze-collect the sample in sterile saline and send at 4˚C within 72 hours.

• First trimester samples: preferred tissue type: identifiable fetal tissue from pathology examination. Otherwise, CVS sample (collected by a specialist prior to evacuation of the uterus- indicate on requisition sample is from IUFD).
• Second trimester or later: Listed in order of preference (where possible): psoas(100mg), liver(100mg), cord(1cm), placenta(100mg). Note: If an IWK autopsy is planned, an appropriate sample will be automatically collected by the pathologist and sent to the Clinical Genomics Lab as part of the autopsy investigation.

Maternal Sample to rule out Maternal Cell Contamination of fetal sample. Either a peripheral blood (EDTA) or Maternal buccal swab can be collected. DNA from peripheral blood is required for some downstream testing. 

Maternal Peripheral blood (separate requisition required): 4mL EDTA tube, separate General Testing requisition also required. 

OR 

Maternal Buccal swab (no separate requisition required) for MCC: Collect two cytobrushes:

1. Wait 1 hour after eating or drinking before collecting. Open package and remove brush without touching any other surfaces.
2. Brush up and down the entire length of the inside of the cheek (at least a 1” path) ten times using firm light pressure. Rotate the handle while brushing to ensure all surfaces of the cytobrush come in contact with the cheek.
3. Return swab back into the package without touching the brush portion to any other surfaces. Repeat the process with a second cytobrush on the opposite cheek.
4. Label both cytobrushes with patient's identifiers, and ship with labelled fetal sample.

Test Methods and Limitations

• For all fetal genetic testing, there is a possibility of test failure due to degraded DNA and/or maternal DNA contamination, especially when testing fetal tissues in the setting of IUFD and early pregnancy loss.
• Targeted Aneuploidy Detection tests only for limited genetic conditions (21, 18, 13, X and Y). Microarray testing looks broadly at an individual’s genetic information for areas of copy number variation (deletions/duplications).