Ultrasound assessment in the first 12 weeks of gestation plays a pivotal role in confirming pregnancy viability, accurately dating gestation, and identifying early markers of fetal and maternal pathology. This lecture provides a comprehensive, practical overview of first-trimester sonography, with a focus on normal developmental appearances and the early detection of anomalies.
The session will begin by reviewing expected ultrasound findings from early gestation, and progressive fetal anatomical development. Emphasis will be placed on optimising transabdominal and transvaginal scanning techniques to ensure diagnostic accuracy and patient comfort. The lecture will explore the role of first-trimester ultrasound in anomaly detection. Early identification of major structural abnormalities, especially with a high detection rate in the first trimester, will be discussed. Case examples will be used to illustrate how deviations can prompt timely referral, further imaging, and appropriate multidisciplinary care.
By integrating current guidelines, evidence-based practice, and real-world imaging examples, this lecture aims to enhance sonographers’ confidence in first-trimester assessment.

Introduction/Objectives: To describe the imaging protocol utilised in our practice for identifying the fourth ventricle choroid plexus during 11–14-week ultrasound examinations, and to evaluate its role as an early marker for posterior fossa abnormalities.
Methods: The fourth ventricle choroid plexus, referred to as the choroid bar, is consistently identifiable during the 11–14week morphology scan. Using either transvaginal or transabdominal ultrasound, the choroid bar can be visualised in multiple cranial planes, including with lateral, dorsal, and ventral insonation. Assessment using transvaginal three-dimensional multiplanar reconstruction is also described, demonstrating the characteristic appearance and features of a normal choroid bar.
Results: Abnormalities in the position and morphology of the choroid bar are indicative of posterior fossa malformations, including Dandy–Walker malformation, open spina bifida, and Blake’s pouch cyst. Representative cases from our practice are presented to illustrate the sonographic features associated with these conditions.
Conclusion: The choroid bar represents a valuable marker in first-trimester morphological assessment for the early detection of posterior fossa abnormalities. Its sonographic features are readily recognisable and can be reliably incorporated into routine imaging protocols by sonographers performing early morphology scans.
Take-Home Message: The choroid bar is a readily identifiable structure on high-resolution obstetric ultrasound between 11 and 14 weeks’ gestation. Incorporation of this marker into standard imaging protocols enhances early detection of posterior fossa abnormalities and can significantly improve clinical management and counselling.