Twin pregnancies require early and accurate determination of chorionicity, as this single distinction fundamentally shapes surveillance, counselling and outcomes. In this session we will focus on the practical ultrasound features that allow sonographers to confidently distinguish monochorionic from dichorionic twins in the first trimester and early second trimester.

The talk will review key diagnostic signs including membrane thickness, the lambda and T signs, placental appearance and cord insertions and highlight common pitfalls that can lead to misclassification. Particular attention will be given to the central role of the sonographer in identifying chorionicity at the earliest opportunity, when diagnostic accuracy is highest.

Once monochorionicity is recognised, the pregnancy enters a different clinical pathway. We will briefly explore the complications unique to monochorionic twins, including twin twin transfusion syndrome (TTTS), twin anaemia–polycythaemia sequence (TAPS), twin reversed arterial perfusion (TRAP), selective fetal growth restriction, monoamniotic and conjoined twins and increased rates of structural anomalies.

Placenta accreta spectrum (PAS) represents one of the most serious complications of pregnancy, associated with significant maternal morbidity and the need for careful antenatal planning. Early and accurate sonographic recognition is therefore critical, with sonographers playing a central role in identifying features that raise suspicion for abnormal placental invasion.
This lecture will provide a practical overview of placenta accreta spectrum, focusing on the key ultrasound markers across gestation.
The aim is to equip sonographers with the knowledge and confidence to recognise concerning findings and contribute effectively to early diagnosis and multidisciplinary care planning.

Assessment of amniotic fluid volume is a key component of obstetric ultrasound and provides important insight into fetal wellbeing and placental function. Abnormal amniotic fluid levels are commonly detected during routine obstetric examinations and may reflect underlying maternal, placental, or fetal pathology. For sonographers, recognising abnormal fluid levels is only the first step; understanding how to systematically evaluate these findings is essential for accurate reporting and appropriate clinical management.

This presentation aims to provide sonographers with a practical framework to identify, assess, and navigate the causes and clinical implications of abnormal amniotic fluid volumes encountered in everyday obstetric practice. It will review the physiology of amniotic fluid production and regulation, followed by an overview of current sonographic measurement techniques, including the single deepest pocket and amniotic fluid index. Common technical pitfalls in measurement will also be discussed.

The causes and clinical implications of polyhydramnios and oligohydramnios will be explored. Polyhydramnios will be discussed in relation to mechanisms such as impaired fetal swallowing, gastrointestinal obstruction, increased fetal urine production, and maternal conditions including diabetes.

Oligohydramnios will be approached using a simplified diagnostic pathway, encouraging sonographers to consider placental insufficiency, fetal renal or urinary tract abnormalities, and rupture of membranes as key mechanisms. Illustrative case studies from our Gold Coast clinical practices will demonstrate real-world examples of both conditions. By focusing on practical scanning strategies and clinical reasoning, this presentation will equip sonographers with a clear framework for recognising, assessing, and navigating abnormal amniotic fluid volumes in clinical practice.

Imaging the brainstem (BS) and measuring the brainstem-to-occipital bone diameter (BSOB) are important components of the first-trimester structural scan. Here are three cases in which subtle deviations in posterior brain spaces during the combined first-trimester scan (cFTS) contributed to later diagnoses of neural tube defects or Dandy–Walker malformation.

Case 1:
A 25-year-old G1P0 (BMI 30) underwent routine cFTS. All views were normal except for non-visualisation of the cisterna magna in the midsagittal plane. Axial images showed a posteriorly displaced aqueduct of Sylvius with the characteristic “crash” sign. The spine appeared normal. At 16-week early morphology, a cystic sacral lesion and ventriculomegaly were identified, leading to a diagnosis of lumbosacral spina bifida.

Case 2:
A 34-year-old G2P1 was referred for tertiary imaging after routine cFTS demonstrated an elevated BS/BSOB ratio and absent intracranial translucency. At 13+4 weeks, the fetus remained prone, with a thickened brainstem and non-visualised cisterna magna. The “crash” sign was again seen, while the spine appeared normal. At 16 weeks, ventriculomegaly and an occipital encephalocele were detected.

Case 3:
A 28-year-old G4P0 had a normal cFTS at 13+5 weeks. At 20 weeks, the cerebellar vermis appeared hypoplastic. Amniocentesis and fetal MRI revealed no genetic abnormalities but confirmed Dandy–Walker malformation, with additional grey-matter subependymal nodular heterotopia and asymmetric ventriculomegaly. Retrospective review showed a decreased BS:BSOB ratio.

These cases highlight the importance of scrutinizing posterior brain spaces in the first trimester, even when definitive diagnosis may only be possible later in gestation.