Mayo Clinic Laboratories > Genetics > Prenatal > Frequently asked questions

Frequently asked questions

Expert answers to frequently asked questions

Prenatal testing can be complicated, but we’re here to help. Our genetic testing experts have provided answers to common questions to simplify the test ordering process.

Does the laboratory need to be notified in advance of sending a prenatal specimen?

  • For routine cytogenetic testing, the laboratory does not need to be notified in advance unless there are complex requests.
  • For molecular testing on prenatal or products of conception samples, consultation with a laboratory genetic counselor is required. Contact us by phone at 800-533-1710.

What are the collection instructions and specimen requirements for prenatal and products of conception samples?

  • Amniotic fluid: Collect in an amniotic fluid container and ship at refrigerate (preferred) or ambient (acceptable) temperature. The first 2 mL of fluid collected should be discarded due to a higher incidence of maternal cell contamination.
  • Chorionic villus: Transfer the CVS sample after collection to a Petri dish containing transport medium such as RPMI or small dish, then transfer to a 15 mL tube containing 15 mL of transport media. Ship at refrigerate (preferred) or ambient (acceptable) temperature.
  • Products of conception (fresh): Attempt to identify and send only fetal tissue for analysis.  Ideally, multiple specimens should be sent, including 1 cm(3) of placenta, and 1 cm(3) biopsy from the thigh muscle/fascia. The laboratory will evaluate all specimens and determine the most suitable for testing. If a fetus cannot be identified, collect 50 mg of villus material or tissue that appears to be of fetal origin. Each specimen should be placed in a separate sterile container with Hank’s solution, Ringer’s solution, or normal saline. All POC specimens can be sent under one order number. Do not send the entire fetus, and do not place samples in formalin. Ship at refrigerate (preferred) or ambient (acceptable) temperature.
  • Products of conception (FFPE): Submit a formalin-fixed, paraffin-embedded block containing fetal or placental tissue. Alternatively, six consecutive unstained, 1-micron-thick sections placed on positively charged slides and one H&E slide may be submitted. A pathology report must accompany each specimen. Ship at ambient (preferred) or refrigerate (acceptable) temperature.
  • Cell cultures: Cultured amniocytes, chorionic villi, or fibroblasts should be shipped in T25 flasks with culture media. Ship at refrigerate (preferred) or ambient (acceptable) temperature.
  • For more detailed information, please refer to the specific test code entry in the Lab Test Catalog.

What are the specimen requirements if I order multiple tests?

  • In general, approximately 20–30 mL of amniotic fluid or 20–30 mg of chorionic villi are sufficient to perform multiple tests.
  • Testing will be attempted on lower volume specimens, but turnaround time may be compromised and there may be a higher risk for test failure.

What information should be submitted to the laboratory for prenatal and products of conception testing?

  • Detailed clinical information is imperative for optimal interpretation of results.
  • For cytogenetic testing, please submit the Chromosomal Microarray Prenatal and Products of Conception Information form (T716).
  • For molecular testing, please submit the Molecular Genetics: Prenatal Patient Information form (MC1235-306).
  • Specific tests may have additional patient information forms to complete. Please see the LTC entries for all required documentation.
  • Please inform the laboratory if the pregnancy was conceived using a donor gamete(s).

Is prenatal testing performed on direct specimen or cell cultures?

  • Chromosomal microarray testing on prenatal specimens (Mayo ID: CMAP) or products of conception (Mayo ID: CMAPC) will be attempted on direct chorionic villi, amniotic fluid, or POC if the specimen meets the criteria (adequate volume, no visible blood present in amniotic fluid). If direct testing is not possible, testing will be performed on cultured cells.
  • Prenatal molecular testing will generally be performed on cultured cells.

What is the cell culture process at Mayo Clinic Laboratories?

  • If direct chorionic villi or amniotic fluid are received, a cell culture will be established.
  • The culturing process takes approximately 2–3 weeks.
  • If cultured cells are received, the specimen will be assessed at Mayo Clinic Laboratories. Additional culturing may be required on arrival depending on cell health and confluence.
  • For all molecular testing, test code CULAF or CULFB will be added by Mayo Clinic Laboratories if not already ordered.
  • For specimens with a CULAF/CULFB order, cultures will be stored at Mayo Clinic Laboratories for a minimum of six months.

Are maternal cell contamination studies required for prenatal and products of conception testing?

Prenatal diagnostic procedures such as chorionic villus sampling and amniocentesis, as well as cases of pregnancy loss, are associated with a risk for maternal cell contamination when the fetal specimen comes into contact with maternal blood or tissue. If maternal cells are present in a fetal specimen, result interpretation can be compromised. As such, it is strongly recommended to perform maternal cell contamination studies with prenatal and products of conception testing to ensure that genetic testing results are representative of the fetus. However, testing will not be rejected if a maternal sample is not received.

How do I order maternal cell contamination studies to accompany prenatal and products of conception testing?

  • To accompany microarray testing (Mayo ID: CMAP, CMAPC, CMAMT), the appropriate code to facilitate maternal cell contamination studies is Mayo ID: PPAP/Parental Prenatal Array Prep Test. Test code PPAP should be ordered only on the maternal blood specimen and must be on a separate order number than the fetal specimen.
    • Specimen requirements for PPAP: 3 mL maternal blood in a lavender top (EDTA) tube and 4 mL maternal blood in a green top (sodium heparin) tube.
  • To accompany prenatal molecular testing, the appropriate test code to facilitate maternal cell contamination studies is Mayo ID: MATCC/Maternal Cell Contamination, Molecular Analysis, Varies. MATCC must be ordered on the maternal blood specimen as well as the fetal specimen. The maternal and fetal specimens must be on separate order numbers.
    • Specimen requirements for MATCC: 3 mL maternal blood in a lavender top (EDTA) or yellow top (ACD) tube.
  • If both microarray and molecular studies are needed, both PPAP and MATCC may be required.
    • Specimen requirements for ordering both PPAP and MATCC: 3 mL maternal blood in a lavender top (EDTA) tube and 4 mL maternal blood in a green top (sodium heparin) tube are sufficient for both tests.

What is the turnaround time for prenatal and products of conception testing?

  • For any testing performed on direct specimen (such as CMAP), please see the Lab Test Catalog entry for estimated turn-around times.
  • For testing that requires cell cultures, an additional 2-3 weeks should be added to the estimated turn-around time listed in the Lab Test Catalog entry.
  • Once a sample has arrived at Mayo Clinic Laboratories, more specific turn-around time estimates can be provided by contacting 800-533-1710.

Can Mayo Clinic Laboratories send prenatal specimens to other labs if a particular prenatal test in not offered in house?

  • If MCL does not offer a specific prenatal test, there are options available to send cultured cells to other laboratories to facilitate testing.
  • If a prenatal sendout test is desired, contact the laboratory of genetic counselors in Cytogenetics at 800-533-1710.

Who should I contact with pricing questions?

  • All pricing inquiries should be directed to Mayo Laboratory Inquiries at 800-533-1710 and will require an account number.
  • Mayo Clinic Laboratories does not currently offer prior authorization services for prenatal or products of conception testing.
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