Clinical Management and Outcomes of Isolated Fetal Pyelectasis Detected at Second‐Trimester Ultrasound: A Retrospective Cohort Study

ABSTRACT Background Isolated fetal pyelectasis is a common finding on second‐trimester ultrasound; however, optimal follow‐up strategies remain variable, often leading to inconsistent use of imaging and specialist services. This study aimed to evaluate clinical management pathways and outcomes and to identify factors associated with persistence. Methods A retrospective cohort study was performed of 221 pregnancies with isolated fetal pyelectasis detected on routine second‐trimester ultrasound within a large tertiary healthcare network. Results Final outcome data were available in 214 cases. At initial third‐trimester follow‐up, pyelectasis had resolved in 167/214 cases (74.2%), increasing to 180/214 cases (84.1%) by final antenatal follow‐up. Persistence was observed in 34/214 cases (15.9%). Male foetuses demonstrated significantly higher persistence rates than female foetuses (20.4% vs. 7.7%; OR 3.07, 95% CI 1.16–8.12, p = 0.022), while persistent cases had larger median renal pelvic diameters than resolved cases (5.6 mm [IQR 5.0–8.0] vs. 4.7 mm [IQR 4.2–5.3], p = 0.0003). Conclusion Isolated fetal pyelectasis demonstrates a high rate of spontaneous resolution, with relatively low persistence on follow‐up imaging. These findings support a more risk‐based approach to follow‐up, with potential to reduce unnecessary imaging and optimise utilisation of specialised fetal diagnostic services.