Association between grade of congenital hydronephrosis and time to natural resolution

Standard of care for pregnancy includes a second trimester ultrasound which may lead to incidental findings of fetal uropathies. The most common fetal uropathy is congenital hydronephrosis (CH). There is limited information regarding the natural history of CH. The objective of this study was to describe factors associated with time to natural resolution of CH.

This is a retrospective cohort study of infants with CH using data from a single hospital's electronic medical record. Between January 2017 and December 2022, infants with CH were identified using ICD-10 codes and were included in the cohort if they had a second ultrasound prior to 2022. Severity of CH was classified using Society for Fetal Urology (SFU) grades. Cox proportional hazards analysis was used to model time to resolution adjusting for age, sex, and initial SFU grade.

Of 209 infants with CH, 126 were included in the cohort, with males predominating (78%). A total of 168 kidney units were included with 84 infants (67%) having only 1 kidney unit affected. In multivariable Cox proportional hazards regression modeling, after adjusting for sex and age at initial ultrasound, initial SFU grade was associated with time to natural resolution (compared to that of grade 1, adjusted hazard ratios for grades 2, 3, and 4 were as follows: 0.59 [95% CI 0.34, 1.01], 0.23 [95% CI 0.12, 0.47], and 0.04 [95% CI 0.01, 0.14]; p < 0.001).

On average, kidney units with not only SFU 4, but also SFU 3, resolved more slowly than those with low-grade hydronephrosis. These findings will assist in counseling parents of children with CH.