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  6. Twin Pregnancy Ultrasound Guideline (330)
Important: please update your RDS app to version 4.7.3

Welcome to the March 2025 update from the RDS team

1.     RDS issues - resolutions

1.1 Stability issues - Tactuum implemented a fix on 24th March which we believe has finally addressed the stability issues experienced over recent weeks.  The issue seems to have been related to the new “Tool export” function making repeated calls for content when new toolkit nodes were opened in Umbraco. No outages have been reported since then, and no performance issues in the logs, so fingers crossed this is now resolved.

1.2 Toolkit URL redirects failing– these were restored manually for the antimicrobial calculators on the 13th March when the issue occurred, and by 15th March for the remainder. The root cause was traced to adding a new hostname for an app migrated from another health board and made live that day. This led to the content management system automatically creating internal duplicate redirects, reaching the maximum number of permitted redirects and most redirects therefore ceasing to function.

This issue should not happen again because:

  • All old apps are now fully migrated to RDS. The large number of migrations has contributed to the high number of automated redirects.
  • If there is any need to change hostnames in future, Tactuum will immediately check for duplicates.

1.3 Gentamicin calculators – Incidents have been reported incidents of people accessing the wrong gentamicin calculator for their health board.  This occurs when clinicians are searching for the gentamicin calculator via an online search engine - e.g. Google - rather than via the health board directed policy route. When accessed via an external search engine, the calculator results are not listed by health board, and the start page for the calculator does not make it clearly visible which health board calculator has been selected.

The Scottish Antimicrobial Prescribing Group has asked health boards to provide targeted communication and education to ensure that clinicians know how to access their health board antimicrobial calculators via the RDS, local Intranet or other local policy route. In terms of RDS amendments, it is not currently possible to change the internet search output, so the following changes are now in progress:

  • The health board name will now be displayed within the calculator and it will be made clear which boards are using the ‘Hartford’ (7mg/kg) higher dose calculator
  • Warning text will be added to the calculator to advise that more than one calculator is in use in NHS Scotland and that clinicians should ensure they access the correct one for their health board. A link to the Right Decision Service list of health board antimicrobial prescribing toolkits will be included with the warning text. Users can then access the correct calculator for their Board via the appropriate toolkit.

We would encourage all editors and users to use the Help and Support standard operating procedure and the Editors’ Teams channel to highlight issues, even if you think they may be temporary or already noted. This helps the RDS team to get a full picture of concerns and issues across the service.

 

2.     New RDS presentation – RDS supporting the patient journey

A new presentation illustrating how RDS supports all partners in the patient journey – multiple disciplines across secondary, primary, community and social care settings – as well as patients and carers through self-management and shared decision-making tools – is now available. You will find it in the Promotion and presentation resources for editors section of the Learning and support toolkit.

3.     User guides

A new user guide is now available in the Guidance and tips section of Resources for providers within the Learning and Support area, explaining how to embed content from Google Calendar, Google Maps, Daily Motion, Twitter feeds, Microsoft Stream and Jotforms into RDS pages. A webinar for editors on using this new functionality is scheduled for 1 May 3-4 pm (booking information below.)

A new checklist to support editors in making all the checks required before making a new toolkit live is now available at the foot of the “Request a new toolkit” standard operating procedure. Completing this checklist is not a mandatory part of the governance process, but we would encourage you to use it to make sure all the critical issues are covered at point of launch – including organisational tags, use of Alias URLs and editorial information.

4.Training sessions for RDS editors

Introductory webinars for RDS editors will take place on:

  • Tuesday 29th April 4-5 pm
  • Thursday 1st May 4-5 pm

Special webinar for RDS editors – 1 May 3-4 pm

This webinar will cover:

  1. a) Use of the new left hand navigation option for RDS toolkits.
  2. b) Integration into RDS pages of content from external sources, including Google Calendar, Google Maps and simple Jotforms calculators.

Running usage statistics reports using Google analytics

  • Wednesday 23rd April 2pm-3pm
  • Thursday 22nd May 2pm-3pm

To book a place on any of these webinars, please contact Olivia.graham@nhs.scot providing your name, role, organisation, title and date of the webinar you wish to attend.

5.New RDS toolkits

The following toolkits were launched during March 2025:

SIGN guideline - Prevention and remission of type 2 diabetes

Valproate – easy read version for people with learning disabilities (Scottish Government Medicines Division)

Obstetrics and gynaecology induction toolkit (NHS Lothian) – password-protected, in pilot stage.

Oral care for care home and care at home services (Public Health Scotland)

Postural care in care homes (NHS Lothian)

Quit Your Way Pregnancy Service (NHS GGC)

 

6.New RDS developments

Release of the redesign of RDS search and browse, archiving and version control functionality, and editing capability for shared content, is now provisionally scheduled for early June.

The Scottish Government Realistic Medicine Policy team is leading development of a national approach to implementation of Patient-Reported Outcome Measures (PROMs) as a key objective within the Value Based Health and Care Action Plan. The Right Decision Service has been commissioned to deliver an initial version of a platform for issuing PROMs questionnaires to patients, making the PROMs reports available from patient record systems, and providing an analytics dashboard to compare outcomes across services.  This work is now underway and we will keep you updated on progress.

The RDS team has supported Scottish Government Effective Prescribing and Therapeutics Division, in partnership with Northern Ireland and Republic of Ireland, in a successful bid for EU funding to test develop, implement and assess new integrated care pathways for polypharmacy, including pharmacogenomics. As part of this project, the RDS will be working with NHS Tayside to test extending the current polypharmacy RDS decision support in the Vision primary care electronic health record system to include pharmacogenomics decision support.

7. Implementation projects

We have just completed a series of three workshops consulting on proposed improvements to the Being a partner in my care: Realistic Medicine together app, following piloting on 10 sites in late 2024. This app has been commissioned by Scottish Government Realistic Medicine to support patients and citizens to become active partners in shared decision-making and encouraging personalised care based on outcomes that matter to the person. We are keen to gather more feedback on this app. Please forward any feedback to ann.wales3@nhs.scot

 

 

Twin Pregnancy Ultrasound Guideline (330)

Please report any inaccuracies or issues with this guideline using our online form

Gestational Age, Chorionicity and Amnionicity

Women should be offered a first trimester USS (< 14+0 weeks) to estimate gestational age and determine chorionicity and amnionicity.

Chorionicity and amnionicity should be determined by the number of placental masses, the presence of amniotic membranes and membrane thickness, the lambda or T-sign.

Clear nomenclature should be assigned e.g inferior and superior, or left and right, in a twin or triplet pregnancy to ensure consistency throughout pregnancy.

If a multiple pregnancy presents after 14+0 weeks then determination of chorionicity and amnionicity could also take into account discordant fetal sex if required.

If TAUSS views are poor because of a retroverted uterus or a high BMI, use a transvaginal ultrasound scan to determine chorionicity and amnionicity.

The largest baby should be used to calculate the estimated date of delivery for the pregnancy.

A photographic record should be placed in the patient’s hospital held records documenting the ultrasound appearance of the membrane attachment to the placenta and an electronic / hard drive record stored. Chorionicity must be checked by senior sonographer

If there is still doubt about the chorionicity, the woman should be referred to medical staff for chorionicity assessment without delay.

Following this if there is still doubt, the pregnancy should be managed as monochorionic until proved otherwise.

Referral should be made for counselling for antenatal screening for combined trisomy (21,18,13) following the diagnosis of a twin pregnancy (fetal medicine at QEUH, Day Care counselling midwife PRM, Screening midwife Clyde). This should ideally be prior to the 11+2 to 14+1 week scan.

The test of choice for twin pregnancies is first trimester combined screening. Every opportunity must be made to maximise the offer of first trimester combined screening. Chance results to be reported are:

  • a term chance of T21 and a term chance of T18/T13
  • a term chance of T21 only
  • a term chance of T18/T13 only

First trimester combined screening will be reported in a dichorionic twin pregnancy as a chance for each fetus whereas in a monochorionic twin pregnancy it will be reported as a chance per pregnancy.

Women who ‘miss’ or have unsuccessful first trimester screening for aneuploidy should be offered second trimester screening for T21. Chance results are reported as a pregnancy related chance that is not fetal specific.

Fetal ultrasound assessment should be performed every two weeks in uncomplicated monochorionic twins from 16+0 weeks onwards until delivery.

Scans at 16 and 20 weeks (detailed anomaly scan) should be performed by a medical sonographer. The detailed fetal anomaly scan should include extended cardiac views (5 standard views).

At every ultrasound, the following should be assessed and recorded:

  • liquor volume (LV) should be assessed in each sac and deepest vertical pool (DVP)
  • Umbilical artery pulsatility index (UAPI)*
  • Fetal bladders should be assessed.
  • Middle Cerebral Artery Peak Systolic Velocity (MCA PSV)

*See Umbilical Artery Pulsatility Index Chart

Increase the frequency of diagnostic monitoring for TTTS in the woman’s 2nd and 3rd trimester to at least weekly if there are concerns about differences between the babies’ amniotic fluid level (a difference in DVP depth of 4cm or more). Include Doppler assessment of the umbilical artery flow for each baby.

Refer for medical scan if LV DVP>8 cm or <2cm before 20 weeks or LV DVP >10cm or <2cm after 20 weeks. If abnormality confirmed discussion with fetal medicine at QEUH is indicated.

Staging of Twin-to-twin transfusion syndrome (TTTS)

Stage Description

I

II

III

IV

V

Poly/oligohydramnios with bladder of the donor still visible

Bladder of the donor no longer visible

Presence of either absent or reverse end-diastolic velocity of the umbilical artery, reverse flow in either twin

Hydrops in either twin

Demise of one or both twins prior to surgery

From 16+0 weeks fetal biometry (HC, AC and FL) should be assessed and abdominal circumference (AC) and Estimated fetal weight (EFW) recorded for each twin. The discordance in EFW should be calculated and documented in monochorionic twins at each visit:

([EFW larger fetus − EFW smaller fetus] ÷ EFW larger fetus) × 100

Increase diagnostic monitoring in the 2nd and 3rd trimesters to at least weekly, and include Doppler assessment of the umbilical artery flow for each baby, if there is an EFW discordance of 20% or more and/or the EFW of any of the babies is below the 10th centile for gestational age.

Refer women with a monochorionic twin pregnancy to a tertiary level fetal medicine centre if there is an EFW discordance of 25% or more and the EFW of either of the babies is below the 10th centile for gestational age because this is a clinically important indicator of selective fetal growth restriction.

Selective intrauterine growth restriction (growth discordance of >20%). Approximately 10-15 % of MCDA twins

Stage Description

I

II

III

Growth discordance but positive diastolic velocities in both fetal umbilical arteries.

Growth discordance with absent or reversed end-diastolic velocities (AREDV) in one or both fetuses.

Growth discordance with cyclical umbilical artery diastolic waveforms (positive followed by absent then reversed end-diastolic flow in a cyclical pattern over several minutes [intermittent AREDV; iAREDV]).

Offer weekly USS monitoring for TAPS from 16 weeks of pregnancy using middle cerebral artery peak systolic velocity (MCA-PSV) to women who pregnancies are complicated by:

  • feto-fetal transfusion syndrome that has been treated by fetoscopic laser therapy or
  • selective fetal growth restriction (defined by an EFW discordance of 25% or more and an EFW of any of the babies below the 10th centile for gestational age)

Aim for delivery between 36+0 and 36+6 for uncomplicated MCDA twins after which point continuing the pregnancy increases the risk of fetal death

For monochorionic monoamniotic twins birth should be planned between 32+0 and 33+6

Fetal anomaly scan can be performed by sonographer if there are no other obstetric reasons for a medical FAS.

Growth USS should be performed every 4 weeks from 24 weeks onwards. Estimated fetal weight, umbilical artery PI and deepest vertical pool of liquor should be measured at each visit.

Fetal weight discordance should be calculated for dichorionic twins:

([EFW larger fetus − EFW smaller fetus] ÷ EFW larger fetus) × 100

Increase monitoring in 2nd and 3rd trimesters to at least weekly, and include Doppler assessment of the umbilical artery flow for each baby if there is EFW discordance of 20% or more and/or the EFW of any of the babies is below the 10th centile for gestational age.

Refer women with a dichorionic twin pregnancy to a tertiary level fetal medicine centre if there is an EFW discordance of 25% or more and the EFW of any of the babies is below the 10th centile for gestational age because this is a clinically important indicator of selective fetal growth restriction.

Aim for delivery between 37+0 and 37+6 for uncomplicated DCDA twins as after this point continuing the pregnancy increases the risk of fetal death.

> 95th percentile is abnormal

(File in notes)

Monochorionic diamniotic twins - antenatal appointments - pdf

(File in notes)

Dichorionic diamniotic twins - antenatal appointments - pdf

Editorial Information

Last reviewed: 24/10/2023

Next review date: 31/10/2028

Author(s): Victoria Watson ST7 PRM, Donna Bean, Lead Sonographer Obstetrics and Gynaecology.

Version: 3

Approved By: Maternity Clinical Governance Group

Document Id: 330

References
  1. NICE [NG137. Twin and triplet pregnancy. 2019.
  2. Khalil A. ISUOG Practice Guidelines: role of ultrasound in twin pregnancy. Ultrasound in Obstetrics and Gynaecology. ISUOG. November 2015.
  3. NHS Fetal Anomaly Screening Programme (FASP). Public Health England. September 2019.