Jane Hanford, Clinical Business Development Manager for Women’s Health Ultrasound at Canon Medical Systems UK, explores the vital role of advanced imaging in managing the complexities of multiple pregnancies. With a focus on ultrasound innovations and precision Doppler imaging, Hanford highlights how high-resolution technology is essential in identifying risks, ensuring accurate monitoring, and supporting positive outcomes in twin pregnancies, where complications such as Twin-to-Twin Transfusion Syndrome (TTTS) demand diligent assessment and early intervention.
As of 2021, 1.6 million twins are born worldwide each year. These pregnancies carry greater risks than singleton pregnancies, including conditions such as premature labour, pre-eclampsia, placenta abruption and foetal growth restrictions, with the potential for further complications depending on multiple types. There are three types of twins: dichorionic diamniotic (DCDA) – each has a separate placenta and separate sac; monochorionic diamniotic (MCDA) – a shared placenta with separate sacs; and monochorionic monoamniotic (MCMA) twins- a shared placenta and sac – this is a much rarer type of pregnancy.
Assessment of the placenta in twins is crucial, and one of the most serious conditions is Twin-to-Twin Transfusion Syndrome (TTTS) – an abnormality of the placenta resulting in an unequal flow of blood – affecting 10 to 15% of monochorionic (MC) twins, with the risk being greater for MCDA twins. Research suggests that MC twins are also at greater risk of additional complications affecting the placenta, including Twin Anaemia Polycythaemia Sequence (TAPS) and Selective Foetal Growth Restriction (sFGR). Left undiagnosed and untreated, these conditions can lead to devastating consequences, making close monitoring throughout gestation via regular, high-quality ultrasound, vital.
The importance of high-end modern equipment
While entry-level2D ultrasound equipment is sufficient in determining multiple pregnancies, and the type of placentation, a high-endultrasound machine providing optimal clarity is recommended to efficiently identify symptoms associated with any anomalies.
In addition to regular monitoring to identify any growth discrepancy in TTTS, sonographers typically look at the amount of fluid each baby has in the amniotic sac by measuring the depth of the deepest vertical pocket. This is to identify if there are any Polyhydramnios or Oligohydramnios. In a recent webinar on the topic, Dr Monique Haak revealed a common pitfall when diagnosing TTTS in MCDA twins, warning that the condition can be easily interpreted as growth restrictions in an MCMA twin pregnancy due to a lack of visibility of the inner membrane. This is where having the most up-to-date equipment, providing fine detail and high-resolution images, is extremely important.
Delving deeper
Should a growth restriction or other abnormality be identified – such as TTTS – then the use of colour Doppler imaging (CDI) technology can enable the sonographer to take a closer look and interrogate the tiny vessels in the umbilical cord and placenta.
Superb Micro-vascular Imaging (SMI) technology is an award-winning Doppler technology proving to be extremely effective in this area. Unlike traditional colour Doppler imaging, which removes clutter from images by suppressing low-velocity components, SMI expands the range of visible blood flow from low to high velocities with incredible sensitivity.
SMI separates blood flow from overlaying tissue motion effectively, while preserving even the subtlest low-flow components with superior detail and definition – meaning that clarity needn’t be sacrificed. SMI is found to be superior in terms of high frame rate, high sensitivity, high resolution, and less motion artefact – making blood flow easier to analyse, especially when visualising the microvasculature flow of the placenta.
Predicting risk
Professor Christoph Lees is currently conducting research, funded by the Medical Research Council and the Wiseman Trust, to understand whether existing ultrasound technology, including SMI, can be used to look at the blood vessels within the placenta of MCDA twins. The study aims to understand how and where they join in predicting the risk of developing TTTS, along with other serious complications.
This ongoing research consists of a study carried out in London in May 2019, which used a Canon Aplio i-series ultrasound machine to map placental angioarchitecture (the arrangement and distribution of blood vessels) in MC pregnancies using different colour Doppler filters. According to Professor Lees, placental angioarchitecture is important to determine the vascular connections in an MCDA twin pregnancy but, up until now, it is rarely examined prenatally. He argues, however, that the detection and characterisation of placental anastomoses (a connection between two structures) within the angioarchitecture could be key to identifying conditions such as TTTS or other risks.
When examining the placental vessels through the different colour Doppler modalities the results varied. While traditional CDI was impacted by sonographic ‘noise’, Advanced Dynamic Flow (ADF), which combined a broadband frequency with a high frame rate, allowed for a more precise depiction of blood circulation, and blood flow to be characterised. With SMI and ADF, Prof. Lees was able to view microscopic blood flow, suggesting its potential for identifying risk earlier in the future.
Overall, the study concluded that a ‘multi-filter’ approach to angioarchitecture sonographic examination (using different colour Doppler techniques) is of fundamental assistance when characterising anastomoses and determining vascular equator in twin MC placentas.
The benefits of early identification
According to guidance as soon as there are signs that TTTS has progressed, the mother will be referred to their regional foetal medicine unit to discuss treatment options. Whilst the options available will depend on the stage of pregnancy, Foetoscopic Laser Ablation is a common, minimally invasive treatment. This procedure focuses on the connections in the placenta causing TTTS, and methodically treats them using a laser.
Innovation within the ultrasound space, however, is providing alternative treatment options. In 2021, doctors at Queen Charlotte’s and Chelsea Hospital, Institute for Cancer Research and Imperial College London, were the world’s first to complete a successful non-invasive procedure using high-intensity focused ultrasound (HIFU) energy to safely treat a case.
For the effective monitoring of twins, and the diagnosis of any complications, the right technologies must be used from the very start i.e. using ultrasound equipment that can deliver crystal-clear images with enhanced resolution. This is important in multiple pregnancies and women’s health in general. Clearer images mean faster examination times and a more confident diagnosis for patients, leading to reduced anxiety and better outcomes.