Abstract

Objective: To clarify the clinical course and appropriate management of undetectable neonatal hydronephrosis during the fetal period.

Study design: We included neonates born in the obstetrics department of our hospital between November 2018 and September 2020. Their urinary system was examined by abdominal ultrasonography. The Society for Fetal Urology (SFU) classification and anterior-posterior renal pelvic diameter (APRPD) were used as parameters to assess urinary tract dilatation. The number of participants, left-right difference in hydronephrosis, male-to-female ratio, incidence of urinary tract infections (UTIs), vesicoureteral reflux (VUR), number of detections, and time course of SFU grade and APRPD were examined.

Results: Totally, 244 patients (146 male, 98 female, 317 kidneys) were examined in this study. The left kidneys of 136 patients and the right kidneys of 35 patients, and bilateral kidneys of 73 patients were examined. UTIs were observed in four cases (1.6%) during follow-up. Patients with UTIs underwent voiding cystourethrography, and VUR was found in two cases. The most frequently detected SFU grade at birth was grade 1 (99.3%), and only two kidneys had SFU grade 2. A total of 171 (54%) patients showed improved hydronephrosis at the age of one month. In addition,307 kidneys (96.8%) showed improved hydronephrosis at 24 months of age.

Conclusion: Most mild prenatal hydronephroses resolve spontaneously. However, hydronephrosis worsens over time in some cases. Cases with APRPD within the interquartile range are considered to have a good prognosis, whereas hydronephrosis exceeding the quartile should be carefully followed.