Down’s syndrome screening quality assurance support service

This document explains the Down’s syndrome screening quality assurance support service (DQASS) and how to use it.

Applies to England

Public Health England (PHE) commissions the Down’s syndrome screening quality assurance support service (DQASS) to support the NHS fetal anomaly screening programme (FASP).


The main aim of DQASS is to monitor and support the quality and effectiveness of Down’s syndrome (T21), Edwards’ syndrome (T18) and Patau’s syndrome (T13) screening in England.

DQASS provides feedback and support to laboratories, sonographers, the Screening Quality Assurance Service (SQAS) and to the FASP. The analyses provided by DQASS are used to improve the performance of the screening programme through feedback on all aspects of the test to laboratories, ultrasound departments and commercial suppliers.

The software used to calculate the T21 and/or T18 and T13 chance result from the biochemical and ultrasound markers is complex and best provided and supported by commercial suppliers. The screening programme has developed a specification for the chance result(s) calculation software for laboratories in England. Software used in screening laboratories must meet the requirements of this specification.

How DQASS works

DQASS works on a rolling audit of screening test data on a 6-monthly cycle. The statistical analyses monitor the screening process at various levels: from the overall standardised screen positive rate (SPR) at the top level, to specific adjustments for ethnicity, smoking and other factors applied to individual biochemical markers. Through meta-analyses, DQASS provides information on effects of factors such as smoking that is used to improve screening performance.

The FASP service specification requires all screening laboratories providing NHS screening to participate in DQASS. The service is provided to screening laboratories and individual ultrasound practitioners across England.

The screening support sonographer

The FASP recommends the provider has a screening support sonographer (SSS) and a deputy SSS with administrative support. These roles oversee the implementation, delivery and monitoring of the ultrasound aspects of the service. The SSS and deputy must actively participate in the DQASS process including submission of a minimum of 25 paired measurements on a 6-monthly basis.

The SSS should:

  • follow FASP requirements as specified in the FASP handbook and by DQASS
  • attend provider and commissioner led antenatal and newborn (ANNB) screening programme boards to represent the ultrasound service, and take the DQASS laboratory and ultrasound summary reports to these meetings
  • put in place an on-going education and training programme for ultrasound practitioners
  • undertake departmental review of ultrasound images including a log of dates that the image review was performed (this is required as evidence for SQAS)
  • keep an accurate and up-to-date database of ultrasound practitioners and associated identity codes and inform DQASS:
    • and the screening laboratory when a new ultrasound practitioner starts, or existing practitioners leave the provider and if known, their new place of work
    • if any of their ultrasound practitioners work at other sites
    • of new trainees to generate a unique identity code
    • of the accuracy of DQASS/Fetal Medicine Foundation (FMF) identity codes and of any changes before the 6-monthly data submission
    • of any omissions or errors in the DQASS reports (detailed ultrasound report for each individual ultrasound practitioner or ultrasound department summary report for each ultrasound provider) so an updated report can be issued if appropriate
  • monitor throughput for each ultrasound practitioner and put in place a locally agreed action plan to enable them to meet the minimum throughput
  • send and provide feedback on DQASS detailed ultrasound reports for each individual ultrasound practitioner
  • implement and monitor any supportive red flag action plans
  • review the SSS resource every 2 years; all new SSS and deputy SSS should review the SSS resource when they start in the role

The SSS should also have a local documented process for the above actions.

DQASS identity codes

Ultrasound practitioners must have a unique identity code matched to the ultrasound department(s) where they work to participate in DQASS.

Trainee ultrasound practitioners

A trainee will need a unique DQASS identity code once they are able to achieve nuchal translucency (NT) and crown rump length (CRL) measurements with minimal guidance from the supervising practitioner.

A DQASS identity code is different from a FMF identity code.

The SSS should email DQASS at with the practitioner’s name and their associated hospital/unit(s) to obtain a DQASS identity code for the trainee.

DQASS will issue an identity code with the suffix ‘T’ to indicate a practitioner in training (for example, 123456T).

The training process should take no longer than 6 months. The training code ‘T’ will remain valid for this time. If training is not completed within 6 months, the SSS should document reasons and contact DQASS.

The trainees should follow the 2-part training process as outlined in education and training for ultrasound practitioners in the FASP handbook.

New ultrasound practitioners from overseas

All new ultrasound practitioners from overseas will require a unique DQASS identity code. The FASP handbook provides guidance to be followed before qualified ultrasound practitioners participate in combined screening.

Ultrasound practitioners who need an FMF identity code to access screening software

Ultrasound practitioners in some departments using specific screening software to calculate the combined screening result need an FMF identity code. In these cases, DQASS will use the practitioner’s FMF code to identify the practitioner and will not issue a separate DQASS identity code. The FMF identity code is issued by the FMF and is a separate process from DQASS.

The SSS should contact DQASS if they have an ultrasound practitioner with an FMF identity code from outside England. This is to make sure that the code is not duplicated with FMF identity codes already used in England.

Data needed for DQASS

Any new screening laboratories, or laboratories wishing to set up a new network, should contact DQASS to register an intention to supply data. Following registration, DQASS will issue a date for data submission.

Laboratories providing NHS screening submit data every 6 months based on the DQASS schedule. It is important that screening laboratories submit data on time (the first working day of the scheduled month) to enable timely reporting and feedback. DQASS should be contacted if data submission is anticipated to be late.

A designated person in each laboratory must provide the data specified for a 6-month period in spreadsheet format with anonymised individual patient data contained in separate rows. Data provided should only include screening performed as part of FASP using either combined screening or quadruple screening testing strategies. Data related to other testing strategies, such as the integrated test, non-routine or private screening arrangements, should be removed by the laboratory before the data is submitted to DQASS.

The laboratory should liaise with the SSS to make sure the ID codes for the sonographers are up to date and that the codes can be matched to an ultrasound department, to enable feedback to be given.

Each column should correspond to a specific data field. The first row should contain the variable label. For the combined test, each row should correspond to a fetus. For the quadruple test each row should correspond to a pregnancy.

If some of the specified data fields are not recorded then a blank column, or a column with N/A in each cell, should be reported. Although it is not used for the statistical analyses, additional information for comparison purposes should include:

  • current medians by day, or regression equation used, indicating both the gestational age and weight adjustment equations used
  • current algorithm parameters, means, standard deviations, correlation coefficients for both the unaffected and affected (T21 and T18/T13) outcomes
  • dates of lot and median changes and corresponding lot numbers
  • calibration or quality-control changes
  • analyser and software used

Any specific queries should also be attached.

Data screening laboratories need to provide to DQASS

Maternal pregnancy characteristics

Pseudo identifier

Maternal date of birth

Maternal age at expected date of delivery

Last menstrual period date

Maternal weight at test date in kg to one decimal place

Smoking: stopped before pregnancy / stopped during pregnancy / smoker

Smoking number per day

Nicotine replacement (e-cigarettes / patches / other) if included in request and available


Diabetes: No / type 1 / type 2

Insulin: Yes / No

Previous trisomies: T21, T18, T13

Twin / singleton

Fetus number (1, 2)

Chorionicity: monochorionic (MC), dichorionic (DC)

Biochemical markers

Blood sample date

Gestational age in days at blood sample date

Alpha fetoprotein (AFP) concentration 1

uE3 concentration 1

Total human chorionic gonadatropin (hCG) concentration 1

Free Beta hCG concentration 1

PAPPA concentration 1

Inhibin concentration 1

AFP multiple of the median (MoM) 2

uE3 MoM 2

Total hCG MoM 2

Free Beta hCG MoM 2


Inhibin MoM 2

1 In cases where biochemical measurements of a particular marker are produced from different instruments, the instrument used should be given in a separate field

2 MoM values should be provided after all corrections for gestation, weight, ethnicity, smoking, insulin-dependent diabetes mellitus (IDDM), twins, have been applied

Ultrasound scan

Scan date

CRL in mm to one decimal place

Head circumference (HC) in mm to one decimal place

NT in mm to one decimal place

Identity code of sonographer and ultrasound department

Chance results

Prior chance for T21

Prior joint chance for T18/T13

Chance for T21

Joint chance for T18/T13

Submission dates for laboratories (start of month)

October and April

Birmingham Women’s NHS Foundation Trust

Mid Essex Hospitals NHS Trust (Broomfield Hospital)

Nottingham University Hospitals NHS Trust

Bolton NHS Foundation Trust

Bolton/Nottingham (BoNo) second trimester network

November and May

Oxford University Hospitals NHS Foundation Trust

Kettering General Hospital NHS Foundation Trust

Barking, Havering and Redbridge University Hospitals NHS Trust (King George Hospital)

Birmingham/King George/Kettering (BKK) second trimester network

January and July

King’s College Hospital NHS Foundation Trust

Sheffield Teaching Hospitals NHS Foundation Trust (Northern General Hospital)

University College London Hospitals NHS Foundation Trust / Medway Maritime Hospital first trimester network

Cambridge/Norfolk and Norwich University Hospitals NHS Foundation Trust (CaNN) first trimester network

February and August

Portsmouth Hospitals NHS Trust (Queen Alexandra Hospital)

Royal Devon and Exeter NHS Foundation Trust

Wolfson Institute of Preventive Medicine

Wolfson/Sheffield second trimester network

March and September

Newcastle Hospitals NHS Foundation Trust

North Bristol NHS Trust (Southmead Hospital)

The Leeds Teaching Hospitals NHS Trust

University Hospitals Coventry and Warwickshire NHS Trust

Cambridge/Oxford/Leeds/Newcastle (COLN) second trimester network

Report types

DQASS undertakes a range of statistical analyses on the data provided and produces reports summarising activity and performance.

Four reports are produced for each 6-monthly data submission. These consist of a:

  • detailed laboratory report for each screening laboratory/network
  • summary laboratory/network report
  • feedback plot (NT/CRL) for each individual ultrasound practitioner
  • feedback plot (NT/CRL) summary report for each ultrasound provider

In addition, 2 national cycle reports are produced at the end of each 6-month cycle. These are the:

  • laboratory/network cycle report
  • ultrasound cycle report

More information about these reports is available in the 6 DQASS report types guidance.

DQASS report recipients

The 6 reports produced by DQASS are sent to numerous stakeholders including laboratory leads, individual sonographers via SSSs, FASP, SQAS (national and regional), public health commissioning teams via regional SQAS. Recipients for each of the reports are as follows:

Detailed laboratory/network report recipients

Laboratory lead

Summary laboratory/network report recipients

Laboratory lead

SSS and deputy


SQAS national and regional

Public health commissioning teams via SQAS

Individual feedback plot (NT/CRL) report recipients

Individual ultrasound practitioners via SSS

FASP (only red flagged data)

SQAS national and regional (only red flagged data)

Feedback plot (NT/CRL) summary report recipients

SSS and deputy


SQAS national and regional

Public health commissioning teams via SQAS

Laboratory/network cycle report recipients (reports published on GOV.UK)

Laboratory lead


SQAS national team

Ultrasound cycle report recipients (reports published on GOV.UK)

SSS and deputy


SQAS national team

Contact DQASS

Down's syndrome screening Quality Assurance Support Service (DQASS)

Room N15
Plymouth Science Park
1 Davy Road


Telephone 01752 764 437



The FASP handbook provides practical guidance to support healthcare professionals and stakeholders in providing the FASP screening pathways.

e-Learning modules

e-Learning modules can be accessed on e-Learning for Healthcare. Relevant modules are:

  • screening for Down’s syndrome, Edwards’ syndrome and Patau’s syndrome
  • first trimester resource for ultrasound practitioners
  • fetal cardiac e-Learning
  • 18+0 to 20+6 week fetal anomaly ultrasound scan resource
  • SSS resource

Nuchal translucency and crown rump length diagnostic plot self-assessment tool

A diagnostic plot self-assessment tool is provided to assist monitoring of NT and CRL measurements. We recommend using it weekly or monthly depending on the number of scans performed. The tool is not designed to be used at the time of the scan to compare measurements to the FMF reference curve.

Software specification

The chance calculation software specification provides details that need to be incorporated into the software package to provide consistent chance results across England. Some variables that are entered into the software are defined by the local user to take account of the reagents used for screening and the characteristics of the local population being screened. These would normally be decided by the laboratory in collaboration with DQASS.

Published 1 January 2014
Last updated 26 April 2022 + show all updates
  1. Added 'Nuchal translucency and crown rump length diagnostic plot self-assessment tool' information to 'Resources' section.

  2. Updated with new information on the screening support sonographer and report types, in addition to submission dates for laboratories to reflect new screening laboratory networks.

  3. Updated list of laboratories under submission date, laboratory network names and other minor DQASS changes.

  4. Added link to laboratory cycle report.

  5. Updated DQASS detailed guide.

  6. First published.