Prenatal Service – South East Scotland Genetic Service

The Prenatal Section provides a diagnostic service to those couples who are at risk of having an abnormal pregnancy.

Sample type depends on gestation: 1st trimester is Chorionic Villi Sample (CVS) and 2nd Trimester is Amniotic Fluid. Patients will have the different testing strategies explained to them, and can agree to QF –PCR studies only, or to both QF-PCR and Microarray (and follow up G-banded chromosome analysis, where appropriate).
For all prenatal samples, a blood sample in EDTA from the mother must be supplied. If a microarray is required, blood samples in EDTA and lithium heparin must be supplied from both parents.

Reasons for referral

Higher chance biochemical result
Higher chance Non-Invasive Prenatal Test (NIPT)
Previous trisomy detected
Family history of known chromosomal rearrangement or single gene disorder
Abnormalities detected on ultrasound scan
Nuchal translucency NT>3.5mm

Referring clinicians are requested to comply with NHS Lothian policy on Mandatory Data Sets: Failure to do so will result in delays in processing or rejection of the sample.

Chorionic Villi Sampling

This involves a biopsy of the chorion cells that form a membrane around the embryo and contributes to the formation of the placenta. This technique is usually performed at 10-12th week of pregnancy and is performed in the clinic by a clinician. The cells are then sent to the Cytogenetics Laboratory for sorting followed by DNA extraction (for QF-PCR/Microarray analysis) and culturing (for possible G-banded karyotyping).

This type of specimen requires contact with the Laboratory at least 24hrs before taking the specimen (telephone 0131 537 1940) to obtain specialised medium.

A prepared ‘cool box’ is sent from the Cytogenetics Department to the referring Antenatal Clinic. The box contains sterile Petri dishes and pastettes, a specialised medium for rinsing and sorting the villus specimen and specialised transport medium in a sterile universal (Sterilin preferred). This box is sent when requested. The media should be removed from the box and stored at 5 degrees celcius. The medium should be allowed to come to room temperature before adding the specimen.

Specimen Tube Requirement:
Sterile 20ml Universal containing transport medium (see above)

Weight of specimen required:
Approx 20-30 mgs of villus is usually required and more if several different tests are to be carried out, i.e. Cytogenetics and DNA analysis.

Please telephone the Department when the specimen has been taken and send by taxi as soon as possible. The CVS must reach the laboratory no later than 3.00pm and should not be sent on a Friday if at all possible.

Amniocentesis

This involves sampling the liquid surrounding the foetus at around 16 weeks gestation. This procedure is performed in the clinic by a clinician. The fluid is then sent to the Cytogenetics Laboratory for DNA extraction for QF-PCR/Microarray analysis and culturing for possible G-banded karyotyping.

Specimen Tube Requirement:
2 Sterile 20ml Universals – Sterilin preferred

        Universal Tube 1        8mls (minimum)  Amniotic Fluid for cell culture

        Universal Tube 2        8mls  Amniotic Fluid (minimum) for DNA extraction

         Lith Hep Tube            3-5mls blood from each parent 

         EDTA Tube                  3-5mls blood from each parent

Please telephone the department when the specimens have been taken and send by taxi as soon as possible. Samples should arrive at the Cytogenetic Laboratory by 2.00pm at the latest if they are to be included in that day’s QF-PCR, otherwise they may not be processed until the following day.

QF-PCR

The laboratory offers a rapid preliminary result on amniotic fluids/CVS for trisomy 13, 18 and 21 by Quantitative Fluorescence PCR within 3 calendar days of receipt.

All Samples

Referral forms can be downloaded from this site or obtained from the laboratory (0131 537 2990). Please fill in all of the relevant clinical details with accurate LMPs and EDDs. Please also send a separate referral form for both parent’s blood samples.

Any special requirements (e.g. Cytogenomics (FISH), or any other testing) must be discussed by telephone with either Head of Service (0131 537 2993) or Head of Section (0131 537 2998) before taking and sending the sample.

It is important that the Laboratory is alerted to the fact that specimens are being sent for analysis. Please telephone 0131 537 1940 or 2998 before sending, giving details of antenatal clinic and of number and names of specimens being dispatched. This way, any missing specimens can be traced.

Arrange for immediate transport to the Laboratory. If this is not possible, refrigerate overnight at (5oC) and send early the following morning.

It should be noted that occasionally, with all these tests, additional work is necessary and delays may occur.

Details of Limitations of Cytogenetic Investigations are available.