Introduction: We aim to compare the ability of the Anteroposterior Pelvic Diameter (APD) vs. Urinary Tract Dilation (UTD) grading systems to predict the rate and time to resolution of hydronephrosis (HN), according to its severity.

Methods: A prospectively collected cohort of patients with prenatal HN was followed from 2008–2021. We excluded patients with hydroureteronephrosis, vesicoureteral reflux, and other urinary tract anomalies. Patients who underwent surgery were censored as non-resolved HN at that time. Each HN grading system was dichotomized for comparison purposes: APD <15 vs. ≥1 5 mm and UTD P1 vs. UTD P2/P3. HN resolution was defined as APD <5 mm or UTD P0 in two consecutive ultrasounds. Kaplan-Meier, Cox regression, and weighted Kappa were used for statistical analysis.

Results: Of 518 patients, 243 (47%) were classified as UTD P1, 192 (37%) as UTD P2 and 82 (16%) as UTD P3. Mean APD and age at baseline were 11.6±7.5 mm and 3.2±2.5 months, respectively. A total of 188 (36%) patients resolved at a median time of 32 months. Analysis of agreement showed 362 of 515 (70%) infants were classified as similar HN severity by both grading systems, and 153 (30%) were UTD P2 or P3 with APD <15 mm (K=0.42, p<0.001) (Table 2). Median time to resolution for different HN grades is presented in Table 1. The overall cumulative resolution rate was 82% and 60% for <15 mm and ≥15 mm APD, respectively. UTD’s cumulative resolution rates were 85% for UTD P1 and 71% for UTD P2/P3 (Figure 1). 

Conclusions: The time to resolution of HN was similar regardless of the grading system used. Both APD and UTD classifications can be effectively applied clinically to counsel patients about resolution trends.