Safe discharge parameters for patients with isolated antenatal hydronephrosis.

INTRODUCTION: Antenatal hydronephrosis is a steady source of urology referrals since the era of routine fetal ultrasonography. Although most resolve, there are no guidelines for follow-up.

OBJECTIVE: Our goal is to define safe parameters with which patients can be discharged early and avoid unnecessary follow-up.

METHODS: We retrospectively reviewed all patients referred to a single children's referral hospital center for isolated antenetal hydronephrosis between 2010 and 2012. We looked at patients and renal units separately and divided the cohort into two groups for comparison. Our analysis endpoint is progression. That is, if the initial postnatal anterior-posterior diameter (APD) is less than 10 mm, progression occurs if the APD increases to 10 mm or above upon follow-up. Conversely, if the initial APD is 10 mm or more in at least one renal unit, progression occurs if the APD remains at 10 mm or above upon follow-up.

RESULTS: There majority of the 186 patients and 308 renal units included in the analysis, were classified in the APD less than 10 mm group. Most renal units in the APD of less than 10 mm group were of SFU grades 0-2 (92.1%) and most of the renal units in the APD of 10 mm or greater group were of SFU grades 3-4 (60%) (Table). Only 19 renal units (6.2%) underwent pyeloplasty, and they were all from the APD of 10 mm or greater group and classified as SFU grade 3-4. No renal unit with an APD of less than 10 mm, nor any with an APD of 10 mm or greater and a SFU grade 0-2 underwent pyeloplasty. More than half of the renal units' hydronephrosis resolved in the APD of 10 mm or greater group, in comparison with 96.1% of the APD of less than 10 mm group. On multivariate analysis, patients with an APD of 10 mm or greater were 7.76 times more likely to show progression (p = 0.0006).

CONCLUSION: An initial postnatal APD of 10 mm or greater, with a SFU grade 3-4, merits follow-up. However, all patients with an APD of less than 10 mm, especially when with a SFU grade 1-2, can be safely discharged as they are unlikely to experience complications.