Avoiding unnecessary intervention in pregnancy: an ultrasound-based decision algorithm for acute flank pain

Acute flank pain during pregnancy presents a diagnostic challenge due to physiological hydronephrosis and the need to avoid ionizing radiation. Clinicians require reliable, non-invasive imaging strategies that guide management and minimize unnecessary intervention. To evaluate high-resolution ultrasonography, including Doppler resistive index (RI) measurement, as a structured decision tool for differentiating etiologies of acute flank pain during pregnancy and guiding management. Retrospective cohort study including 87 pregnant women presenting with acute flank pain between May 2022 and December 2023.Patients underwent detailed clinical, laboratory, and high-resolution US evaluation: B-mode grading of hydronephrosis, renal parenchymal and perinephric assessment, ureteric and bladder evaluation, and intrarenal arterial Doppler RI measurement. Clinical parameters including pain severity, fever, and inflammatory markers (CRP, WBC) were integrated to support imaging findings Ultrasonographic findings were correlated with clinical course and management outcomes. Hydronephrosis was detected in 96.5% of patients, predominantly right-sided (77%). Hydroureteronephrosis with Collecting system wall thickening and edema suggestive of inflammation was the most common etiology (75%). Urolithiasis was detected in 23% of patients, high grade obstruction confirmed in 11.5%. Patients with high grade obstruction had elevated intrarenal RI (≥ 0.72; mean 0.78), whereas those with physiological ureteral compression had normal RI with preserved ureteric jets. Conservative management succeeded in 91% of cases; 9% required surgical intervention. High-resolution US combined with Doppler RI provides a safe, reproducible, and management-oriented decision algorithm for acute flank pain in pregnancy. It differentiates physiological from pathological obstruction, supports conservative management in most patients, and identifies those requiring timely intervention.