Prenatal testing

The Synnovis Genetics laboratory at Guy’s Hospital is the hub laboratory of the SE GLH. 

For accredited tests refer to the UKAS website here UKAS: Search Accredited Organisations – UKAS number 8688. The laboratory works closely with Clinical Services throughout Guy’s and St Thomas’ NHS Foundation Trust (GSTT) and St George’s Hospital Foundation Trust. With our partner laboratories, the SE GLH provides a comprehensive genetics service for a population of 8 million.

In addition, the laboratories receive a large number of national and international referrals for an increasing number of highly specialised genetic tests.

As well as providing a comprehensive diagnostic service, the Synnovis Genetics Laboratory has an active research and development programme. The laboratory works collaboratively with other groups such as GSTT Biomedical Research Centre, GSTT Genetics Innovation Unit and the GSTT Assisted Conception Unit for Preimplantation Genetic Diagnosis.

Tests offered

QF-PCR rapid aneuploidy detection for chromosomes 13, 18, 21.  Testing for sex chromosome aneuploidy if clinically indicated. Commonly requested indications include:

  • R401.1 Common aneuploidy testing – prenatal
  • R320.1 Invasive prenatal diagnosis requiring fetal sexing
  • R22.1 Fetus with a likely chromosomal abnormality – PCR
  • R21.1 Fetal anomalies with a likely genetic cause – PCR

Targeted G-banded karyotype follow-up of abnormal PCR results.

More information about this QF-PCR testing is available on the Synnovis website

Array analysis if clinically indicated (e.g. NT >3.5mm before 14 week gestation, nuchal fold >6mm between 14-20 week gestation, fetal ultrasound anomalies). Commonly requested indications include:

  • R22.2 Fetus with a likely chromosomal abnormality – microarray
  • R21.3 Fetal anomalies with a likely genetic cause – microarray

More information about this array testing can be found on the Synnovis website.

PND targeted analysis for carriers of balanced chromosome rearrangements or known familial imbalances where clinically indicated.

Cell culture and DNA extraction for indicated monogenic disorder testing and/or fetal whole exome sequencing [WES]. Some monogenic tests, and all cases referred for fetal WES, will require DNA to be sent to another GLH for testing.

  • R21.2 Fetal anomalies with a likely genetic cause – WES

Please refer to the NHSE National Genomic Test Directory for further indications available and information regarding clinical criteria.


Sample types accepted:

  • 20ml amniotic fluid in a dry sterile container
  • 20mg chorionic villus sample in transport medium (contact the laboratory for provision of sample containers)
  • Fetal blood samples
  • DNA samples

Please notify the laboratory before sending prenatal samples by e-mailing

Testing of low volume samples may need to be prioritised. If direct DNA extraction is not possible, testing will be performed on cultured cells which may delay the turnaround time.

Please send maternal blood with bloodstained amniotic fluid samples for maternal cell contamination (MCC) testing. Samples with a high level of MCC will not be suitable for testing.

If samples are unlabelled the referring clinician will be contacted to complete a disclaimer form for consent to process the sample.

Turnaround times

Rapid aneuploidy by QFPCR – 3 days

Prenatal testing for monogenic disorders – 3 days (known familial variants)

Prenatal targeted G-banded karyotype (follow up of abnormal PCR) – 14 days

Prenatal Array analysis – 14 days

SE GLH: Non-WGS Genetic test request form​

Please send an accompanying full ultrasound scan report with all prenatal samples. 

Please note that any errors made when completing the form may result in delays in processing. 

It is the referring clinician’s responsibility to ensure that the patient/carer knows the purpose of the test and that the sample may be stored for future diagnostic testing. 

SE GLH: Record of Discussion form

The Record of Discussion form can be downloaded and used to guide and record the patient’s consent. This should be saved in local patient records and does not need to be sent with the request form.

Fetal WES service

Prior to referral, all fetal WES requests should be discussed with your local Clinical Genetics team at either Guy’s and St Thomas’ NHS Foundation Trust (GSTT) or St George’s University Hospitals Foundation Trust.

If the pregnancy is going to continue please request a rapid WES on teh fetal sample, if the pregnancy is not going to continue please request a non-urgent WES on the fetal sample.

Parental blood samples are required for testing (5ml in EDTA).

Further documentation to be completed:

Rapid WES

Non-urgent WES

For fetal exome queries please email

Lab address and opening hours

Genetics Laboratory
5th Floor Tower Wing
Guy’s Hospital

Mon-Fri 9:00-17:00
Tel: 020 7188 2582

Key contacts

Service Delivery Manager – Keeley Monsen-McCann 
Operations Lead – Emma Fowler

For any clinical or scientific queries please contact the laboratory on 020 7188 1713 between the hours of 9am to 5pm, Monday to Friday. Alternatively contact Emma Fowler on 020 7188 1712.

For complaints

For complaints, please visit the Synnovis complaints page for the policy and procedure.

With any Whole Genome Sequencing (WGS) test ordered, a Record of Discussion (RoD) form will also need to be submitted. This document is to record the patient’s consent for genomic testing and their choice on taking part in research. Guidance on the patient choice conversation can be found here
This RoD form will be available for clinicians to download from this webpage. Once completed with the patient, it can be send to the lab with the corresponding test order form and sample.
Tests available to order will be listed in the National Genomic Test Directory. A test order form will soon be made available for clinicians on this webpage to download and complete. This form will include the address of the laboratory that the appropriate sample and completed form needs to be sent to.
Until the new Genomic Laboratory Service goes live, please continue to follow existing test order processes.
Later this year, the online test ordering tool for Whole Genome Sequencing will be integrated into the National Genomics Informatics System (NGIS) and clinicians will be able to search or filter to find a clinical indication, confirm eligibility criteria and start the test request process for their patient.