Cytogenetics Website
Prenatal Diagnosis
Reasons for Referral
Increased risk of chromosome abnormality, including:
• Abnormal ultrasound scan
• Advanced maternal age (35+)
• Increased risk following biochemical screening
• Parent carries a chromosome rearrangement
• Previous child with a chromosome abnormality
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 and what the transport requirements are. Costs of tests carried out elsewhere as well as transport costs are usually passed back to 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
• Samples should be addressed to
Cytogenetics Unit,
St. James’s Hospital
Beckett Street,Leeds
LS9 7TF
• 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 4°C (in a refrigerator).
• Please try to avoid sending samples at weekends or bank holidays.
ALL PACKAGES MUST CONFORM TO POST OFFICE REGULATIONS
(Copies are available from the Post Office)
Sample Requirements
Amniotic Fluids
• 10-20mls of fluid in a sterile, leak proof, plain (no anticoagulant), plastic universal container.
• A completed prenatal referral card should 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. Referral cards are available on request.
• Samples must reach the laboratory by 3pm for a rapid 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 media, supplies of which can be obtained from 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 DNA or biochemical testing, cytogenetic studies will only be performed if there are sufficient villi.
• Any samples referred for cytogenetics investigations where there are insufficient villi for both direct and cultured preparations will usually be processed by long-term cultures only.
• A completed prenatal referral card must accompany all samples.
Foetal Blood Samples
• Foetal blood samples should be collected into 2ml paediatric lithium heparin tubes.
• 0.5 - 1.0ml is usually sufficient.
• Samples should be accompanied by a completed cytogenetics referral card. Please state that the sample is foetal blood.
Maternal Blood samples
• A maternal blood sample in EDTA should accompany all prenatal invasive samples to help with interpretation of the results.
Reporting of Results
• Amniotic fluid and Chorionic villi: The reporting times are dependent upon rate of cell growth in culture, but generally results are available in 2 weeks. These are sent to the referring clinician.
• Results obtained from direct preparations of chorionic villus and from rapid tests on Amniotic Fluid are usually available the following day (as long as the sample was received early enough for processing). These are telephoned to the referring clinician or designated contact (eg screening coordinator).
• Cytogenetic results from direct CV preparations are provisional, a final report is only issued once the longterm cultures have been analysed.
• Foetal blood samples 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.
• Reports on chromosomally abnormal results are usually telephoned to the referring clinician or designated contact, and the interpretation discussed where appropriate.
• Abnormal results are faxed on request, to a secure fax number. Normal results are not usually faxed.
• Where abnormal results are complex or ambiguous, copies may be sent to the Clinical Genetics Unit if this is considered appropriate.
•A sample for confirmation is requested on all cases where termination of pregnancy occurs following the prenatal detection of an abnormal karyotype.
•Maternal cell contamination is a limitation of amniotic fluid and chorionic villus culture. If unrecognised, this may lead to a misdiagnosis.
•Currently all amniotic fluid samples are tested for trisomy 13, 18 and 21 using Qf-PCR. Full karyotyping is only carried out on cases of clinical need eg abnormalities on scan, family history of chromosome abnormality, discoloured samples.
•A small number of prenatal samples will fail to initiate cell growth. A repeat sample will be requested.
•Conventional cytogenetic prenatal diagnosis may fail to identify small cytogenetic abnormalities or chromosome mosaicism.
Last Updated 27/07/06