582 - Higher value follow-up for mild antenatal urinary tract dilation: How many additional ultrasounds?

Publication Number: 2567.582

Erika Luis, Children's Hospital at Dartmouth-Hitchcock, Sunapee, NH, United States; Elizabeth Ferrara, Children's Hospital at Dartmouth-Hitchcock, Lebanon, NH, United States; Daniela Ruelas Lomeli, Dartmouth College, Hanover, NH, United States; Alison Holmes, Geisel School of Medicine at Dartmouth, Etna, NH, United States

Background: Urinary tract dilation (UTD) is a common finding on antenatal ultrasound, yet there is scant evidence on optimal postnatal follow-up. The majority of mild antenatal UTD (4-7mm in the second trimester or 7-10mm in the third trimester) is transient and physiologic, resolving either pre- or postnatally. AUA (2014) and AAP (2025) guidelines recommend subspecialty referral and two follow-up renal ultrasounds (RUS) for newborns with mild UTD persisting into the third trimester. Evidence supporting the value of the second follow-up postnatal RUS is weak, and subspecialty resources are limited, with a shortage of pediatric nephrologists.

Objective: In the setting of persistent mild antenatal UTD, we sought to determine if the second postnatal RUS adds additional diagnostic value in cases where the first postnatal RUS is normal. We also describe the eventual outcomes of all cases of third-trimester mild antenatal UTD in a ten-year period and examine related subspeciality referral patterns.

Design/Methods: We reviewed charts of all infants undergoing postnatal RUSs for evaluation of antenatal mild UTD (7 -10 mm) on a third-trimester ultrasound between 1/1/2015 and 8/31/2024 at a center that had implemented the 2014 AUA guideline by the end of 2014. Classification of UTD was based on the radiologist/perinatologist's RUS measurements or classification. We summarized the numbers of postnatal RUSs, subspecialty visits, and eventual progression of any renal disease.

Results: Of 115 neonates (81% male), 30 (28%) had a normal first postnatal RUS, 72 (63%) had persistent mild UTD, and 13 (11%) progressed to moderate UTD. No patients progressed to severe UTD. Classification of patient outcomes, subsequent imaging, and subspecialty utilization are found in Table 1. Of the 30 patients with a normal first RUS, none progressed to clinically significant renal disease. In those with mild postnatal UTD, 63 (88%) never progressed further. There were 162 potentially unnecessary subspecialty visits for patients who only had mild UTD. In the moderate UTD group, 8 normalized, 2 stabilized, and 3 are resolving. One had surgery for ureteropelvic junction obstruction.

Conclusion(s): Mild UTD is a transient, benign, physiologic state that rarely progresses. Infants with a normal first postnatal RUS may not need a second study. Persistently mild, non-progressive UTD could be managed in primary care, reserving subspecialty referral for worsening UTD or additional concerns.

Table 1
Description of cases and resource utilization based on urinary tract dilation classification on the 1st postnatal renal ultrasound (RUS).