Skip to main content
Smaller Larger Print

MENU

Prenatal testing

Chromosome studies are requested where pregnancies are identified as being at risk of a cytogenetic abnormality.

Risks may include:

  • advanced maternal age;
  • positive maternal serum screening;
  • fetal abnormalities found on ultrasound;
  • where a parent is a known carrier of a chromosome anomaly,
  • where a high risk trisomy has been found by NIPT.

Samples

Amniotic fluid – 10ml+ in a plain sterile, leak-proof container. Suitable containers can be provided by the laboratory. The specimen must not be frozen. See sample stability section for cytogenetic samples.

Chorionic villus – 5mg+ in sterile transport medium. Suitable containers containing medium can be provided by the laboratory. The specimen must not be frozen. See sample stability section for cytogenetic samples.

Fetal blood – 1–2ml lithium heparin whole blood, gently mixed to prevent clotting. The specimen must not be frozen. For QF-PCR or array CGH, please provide EDTA whole blood.

See sample stability section for cytogenetic samples.


Turnaround time

This is dependent on the rate of cell growth; however, the usual turnaround time is approximately 2 weeks. As invasive prenatal diagnosis becomes less common, a number of circumstances now occur more frequently that may result in delayed reporting time.

These include:

  • A delay in transportation in order to collect a batch of samples to reduce courier costs. Even when couriered promptly, sample growth may be slower than that seen in samples sent immediately.
  • Sampling at early or late gestations, for example to confirm non-invasive tests or follow up anomaly scans.
  • A tendency to take smaller quantities of sample or to take insufficient sample for multiple techniques.
  • The request for karyotyping as an add-on after an initial PCR test.


Fetal blood results will usually be reported by 10 calendar days. For all other prenatal tests, please contact the laboratory prior to taking samples.


Notes

  • Maternal contamination, and mosaicism may complicate the analysis and may lead to the suggestion that a second invasive test is performed.
  • Rarely, cultures fail to grow (overall <1%)
  • Very small chromosome abnormalities may not be detected.
  • For Twin to Twin Transfusion samples or heavily bloodstained amniocentesis samples, please provide a maternal EDTA blood sample for comparison studies.