Appropriate timing for performing abdominal ultrasonography and termination of observation follow-up for antenatal grades 1or 2 hydronephrosis

Abstract Background: Most cases of antenatal Society of Fetal Urology (SFU) grades 1 or 2 hydronephrosis (HN) improve or resolve spontaneously with conservative treatment. However, there is no consensus on the duration of follow-up for grades 1 or 2 HN. The aim of this study was to determine the need for a continuous follow-up period and to propose a new follow-up protocol for children with antenatal grades 1 or 2 HN.Methods: Subjects underwent ultrasonography examination according to the SFU classification. We retrospectively evaluated data from 112 patients with postnatal grade 1 HN and 69 with grade 2 HN diagnosed between January 2010 and December 2017. We examined the change in HN grades using serial ultrasonography. The Kaplan-Meier method was used to show the effect of HN grade on the rate of HN changes.Results: The mean follow-up duration was 44.9 ± 36.4 months (range, 12–274 months). Initial SFU grade 1 HN disappeared in 47.0% of cases at 12 months, 66.4% at 24 months and 73.2% at 48 months. Initial SFU grade 2 HN improved in 74.7% of cases at 12 months, 88.3% at 24 months and 89.5% at 48 months. However, 14.6% of SFU grade 1 and 2.8% of SFU grade 2 cases increased in grade, and 99.3% of these cases worsened within the first 6 months. No cases with increased grade required pyeloplasty. Initial disappearance and later reappearance of HN occurred in 40.5% of SFU grade 1 and 2 cases. The mean duration of later reappearance was 39.1 ± 36.2 months (range, 12–137 months). No reappearance was detected after more than 1 year.Conclusions: Ultrasonography within the first 6 months was necessary for management of children with antenatal grades 1 or 2 HN because some patients showed worsening. Thereafter, it was considered safe to increase the follow-up intervals for stable cases. Most cases resolved spontaneously; however, a few cases reappeared within 1 year. Therefore, ultrasonography after 1 year was necessary for children with HN that had spontaneously disappeared. The appropriate time to terminate follow-up was considered to be 1 year or more after HN disappearance was confirmed.