[CG] Fetal Anomaly Screening (FAS) Scan


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Fetal Abnormalities Detection Ultrasound Scan Gestation 18-20 +6 Weeks

A routine fetal anomaly screening appointment scan should be 30 minutes which should include ‘on and off the couch time’ as well as time to complete the report.

The equipment used should be  machines purchased primarily to implement the screening programme and preferably be no more than 5 years old.

The FAS scan will be completed between 18–20+6 weeks gestation but will be targeted at a gestation of 20weeks.  This allows time for referral and intervention before 24 weeks if required.


Ensure that written consent has been obtained and documented. Prior to beginning the scan, give an explanation of the scans purpose and its limitations.

Obtain verbal consent to continue.

Check List

On Green sheet (Appendix A)

Ensure ID sticker attached

Patients will be given up to two attempts to obtain the entire checklist, unless an abnormality is suspected.

Please note on the report the reason for a second attempt, e.g. poor fetal lie, increased maternal BMI etc. 

The sonographer carrying out the repeat scan needs only to check the areas that have not been seen on the initial scan (and will only be responsible for this structure(s)). It is at the Sonographers discretion if they wish to examine the fetus fully again, however they have to bear in mind the ALARA Principle.

If after two attempts the scan still remains incomplete give an explanation to the patient and reiterate the limitations of scanning. This should then be documented on the scan report the reasons for incompletion and that it has been discussed with the patient.  

All measurements are required to be in millimeters.

Where structures are indicated in the plural, only one tick is required to indicate both were seen, or in the case of limbs that all three long bones were seen, for each side.  If there is a unilateral anomaly, do not tick the box.  Use   The  comments section to say what side is seen and normal and then give an explanation of the other sided anomaly.

If any anomaly is seen, use the comments box to explain your findings.

If the fetal biometry < 5th centile then a further growth scan should be arranged in 2 weeks.  At the second scan if growth is still <5th centile refer for a medical scan in a further 2 weeks.  Assuming the patient will be 24 weeks medical staff can put a management plan into place.  


The following structures must be identified and assessed 




  • shape
  • mineralization
  • brain – review all intra cranial anatomy


  • lips and nostrils


  • position
  • size
  • 4 chamber view
  • right outflow tract
  • left outflow tract


  • integrity


  • stomach position and size
  • bowel – echogenic; double bubble
  • abdominal wall integrity


  • number
  • position
  • echogenicity
  • absent
  • dilated/ pyelectasis etc.


  • must be seen
  • absent
  • dilated


  • whole spine, including sacrum – integrity/ossification etc.
  • sagittal
  • coronal
  • transverse
  • skin line

Upper Limbs

  • 3 long bones each limb


  • both hands, metacarpals present; not counting fingers

Lower Limbs

  • 3 long bones each limb


  • both feet, metatarsals present; not counting toes

Amniotic Fluid

  • subjective assessment.  Only report and refer if abnormal.
  • Remember to check stomach, kidneys and bladder.


  • size and location
  • If placenta appears to completely cover the internal os, rescan as per each departmental protocol in 3rd Trimester.
  • All previous Caesarean section patients with an anterior placenta must have a scan arranged for placentography to exclude placenta praevia and accreta  as per departmental protocol.


Echogenic Bowel

  • Only comment and refer to medical staff if density equivalent to bone.

Normal Variants

  • Do not comment on a placenta shelf or amniotic sheets.
  • Do not comment on presence of choroid plexus cysts.
  • Do not comment on cardiac echogenic foci (Golf Balls).
  • Do not report on ‘soft markers’.

Measurements Required   

Head Circumference

Transcerebellar Diameter

Ventricular Atrium

Abdominal Circumference

Femur Length


Renal Pelvis – AP diameter inner to inner.  Renal Pyelectasis - >5mm follow departmental protocols.

Images to be Taken

  • Head Circumference
  • Atrium of the lateral ventricle including measurement
  • Transcerebellar Diameter
  • Coronal view of lips with nasal tip
  • Cord insertion
  • Abdominal Circumference (which incorporates stomach)
  • Kidneys (Transverse section)
  • Femur Length
  • Spine – sagittal view to include sacrum and skin covering
  • Profile

Any anomaly, suspected anomaly or low lying placenta must be imaged.

CLYDE, QEUH and PRM – All images to be inserted into the brown image envelope within the hospital case notes.

Referral Pathway

It is good practice for the sonographer to seek a second opinion. In the first instance, a senior member of staff must be consulted before referring to medical staff.

If a fetal anomaly is suspected during an anomaly screening scan then the woman should be informed at the time of the scan or shortly afterwards. This should occur in privacy and ideally, if the woman wishes, in the company of a partner, friend or relative.


Enter your report on page titled ‘Your ultrasound scans’.

Complete the Scan section – score out Detailed scan and put in ‘Routine FAS’. In the space provided, if it is a normal scan, write ‘no obvious abnormality seen’.

If the scan is incomplete, write incomplete scan and reason, i.e. fetal spine not seen, poor view due to fetal lie etc. Record  “review 1-2/52”  and update track care accordingly.

Write down placental location.

Appendix A: Example of completed Fetal Anomaly Screening – Ultrasound Report NHS GG&C

Last reviewed: 28 July 2016

Next review: 31 August 2021

Author(s): Donna Bean, Lead Sonographer, Glasgow; Dr. A. M. Mathers, Consultant Obstetrician on behalf of GONEC Group

Version: 2

Approved By: Dr Catrina Bain, Clinical Director