Antenatally diagnosed hydronephrosis and determinants of spontaneous resolution

Antenatal hydronephrosis (ANH) is the most common finding on prenatal ultrasounds occurring in 1–5% of pregnancies. Despite its high prevalence, there is a lack of defined predictors for recovery. We investigated correlations between spontaneous resolution of ANH and confounding determinants. A retrospective outpatient review study was conducted from 2012 to 2017. The inclusion criterium was ANH of any severity, exclusion criteria were lost to follow-up, no prenatal diagnosis or surgical intervention < 12 months. Recovery was defined as an anteroposterior diameter ≤ 10 mm. Data were analyzed using Pearson Chi-square or Fisher’s exact test and correlations between recovery and confounders were analyzed using Spearman correlation coefficients. In our study, 237 newborns had hydronephrosis (4.6% of the outpatients, n = 5117), 38 newborns were excluded ( n = 29 failed prenatal diagnosis, n = 5 lost to follow-up, n = 4 surgical intervention < 12 months). Most neonates ( n = 186, 93.5%) showed a spontaneous resolution within 1 year, with 94.1% <2 months. Males were more prevalent ( n = 156 vs. n = 43), but it did not correlate with recovery ( p = 0.738). In the cohort, 40 (20.1%) had a relevant comorbidity and this group was less likely to recover spontaneously (congenital anomaly r s = -0.273, p = 0.001; infection r s = -0.283, p = 0.002). ANH is common, but most infants had a spontaneous recovery. Neonates with comorbidities including infection were less likely to recover spontaneously. These findings could guide clinicians in their follow up plans and reassurance of parents. Validation of these findings should be confirmed in future studies.