The Leeds Teaching Hospitals NHS Trust

Prenatal Diagnosis

Reasons for Referral

Increased risk of chromosome abnormality, including:

  • Abnormal ultrasound scan
  • Increased risk following screening, (biochemical or ultrasound)
  • Parent carries a chromosome rearrangement
  • Previous child with a chromosome abnormality

Samples are also accepted from patients whose pregnancy is at risk of a non-chromosomal genetic or metabolic disorder. These patients should usually be referred through the Dept of Clinical Genetics at Chapel Allerton Hospital, Leeds and as much advance notice as possible must always be given to the laboratory.

Please Note:

Please state clearly on the referral card if a test other than standard Cytogenetics is required, for example testing for cystic fibrosis where there is a scan finding of echogenic bowel.

If any of the original sample or cultured cells are to be forwarded to another laboratory, please state this on the referral card, giving details of where the sample is to be sent, what test is required, and what the transport requirements are. Costs of tests carried out elsewhere as well as transport costs are usually met by the referring clinician.

If possible patients with a family history of a chromosome or other relevant genetic abnormality should be screened by the investigation of parental blood samples before prenatal diagnosis is undertaken.

Sample Transport

Please see contact page for laboratory address and contact details.

Cytogenetic analysis requires living cells. Please ensure that the sample reaches us as quickly as possible (preferably within 24 hours). First class post is satisfactory.

Samples should not be frozen or exposed to excess heat. If there is a delay in transit please store the sample at 4C (in a refrigerator).

Please try to avoid sending samples at weekends or bank holidays.

When sending samples by post a secure container should be used to conform to current postal regulations, i.e. P650 and UN3373 applicable. For more information please see here.

Sample Requirements

Amniotic Fluids

10-20mls of fluid (15-20mls if SNP array testing is required - see later for further details) in a sterile, leak proof, plain (no anticoagulant), plastic universal container labelled with at least two unique patient identifiers (name, NHS number, date of birth, hospital number)

A completed constitutional testing referral form must accompany all samples. It is important that all information requested on the card is supplied by the referring hospital; failure to provide relevant information may result in delays in reporting results.

Samples must reach the laboratory by 3pm for a rapid (QFPCR) result to be available the next working day.

Chorionic Villus Samples (CVS)

CVS should be received on the same day taken and preferably no later than 4pm.

CVS must be sent in transport medium, details of which can be supplied by the laboratory.

Cytogenetic studies are performed on CVS with an optimal size of 10mg or more. For other investigations such as DNA or biochemical investigations, 20mg or more are preferred.

Where samples have been referred primarily for SNP array, DNA or biochemical testing, cytogenetic studies will only be performed if there are sufficient villi.

A completed constitutional testing referral form must accompany all samples as for amniotic fluids, above.

Fetal Blood Samples

Fetal blood samples should be collected in to 2ml paediatric lithium heparin tubes.

0.5 - 1.0ml is usually sufficient.

Samples should be accompanied by a completed cytogenetics referral form, as above.

Please state that the sample is fetal blood and whether or not the pregnancy is ongoing.

Maternal blood samples

A maternal blood sample (2-3ml in EDTA) should accompany all prenatal invasive samples to help with the interpretation of rapid results.

For requirements for parental karyotyping, please refer to separate user guide for postnatal samples.

Sample Processing

Amniotic fluid and chorionic villus samples will be tested using QFPCR for 13,18,21, X&Y. Samples will only be fully karyotyped in the event of an abnormal result.

Rapid FISH testing may be undertaken in addition to QFPCR for fetal heart defects detected on the 20 week anomoly scan.

Direct karyotype from chorionic villus material will be performed in cases which require a rapid full karyotype e.g. family history of a balanced chromosome rearrangement.

Following a normal QFPCR result, any pregnancy with an increased NT (>3.5 mm) or an abnormality detected on ultrasound scan will be eligible for SNP array testing.

Reporting of Results

Results obtained from QFPCR testing (of both CVS and amniotic fluids) and direct CVS preparations are usually available the following day as long as the sample was received early enough for processing. Cytogenetic results from direct CVS preparations are provisional, a final written report is only issued once the long term cultures have been analysed.

SNP array results will be available within 14 days unless DNA needs to be extracted from cultures which will delay the reporting time. The clinician will be contacted in the event of this happening to advise of the delay.

Fetal blood karyotype results are usually reported to the referring clinician within 4-5 working days following receipt of the sample. A provisional result may be available in 48 hours.

Amniotic fluid and CVS (full karyotype): The reporting time is dependent upon rate of cell growth in culture, but generally results are available in 2 weeks. These are sent to the referring clinician and will mostly be confirmations of abnormal QFPCR findings.

All rapid (QFPCR, direct CVS & FISH) and SNP array results will be emailed to the referring clinician and/or designated contact (eg screening co-ordinator).

Where abnormal results are complex or ambiguous, reports may also be sent to the Clinical Genetics Unit if this is considered appropriate.

Please note we no longer require a follow-up sample at delivery / termination for confirmation of abnormal prenatal results.

Maternal cell contamination is a limitation with amniotic fluid and chorionic villus culture. If unrecognised, this may lead to a misdiagnosis.

Prenatal SNP array Testing - 'Information for the Clinician'

For further information please click for the user guide.