Validation of “urinary tract dilation” classification system: Correlation between fetal hydronephrosis and postnatal urological abnormalities

Aim to illuminate the correlation between fetal hydronephrosis and postnatal urological abnormalities by a new classification system—“urinary tract dilation (UTD)” grade. Of 659 pregnancies screened by ultrasound, 34 cases were found with isolated fetal hydronephrosis, and enrolled in our study from 2017 to 2019. These 34 infants had been prospectively followed up to 6 months after birth by 3 times of urinary tract ultrasound. Hydronephrosis was graded in accordance with the UTD classification system. Among 34 infants with isolated fetal hydronephrosis. Twenty-four (70.6%) were classified as UTD A1 grade (mild hydronephrosis), and the other 10 (29.4%) were UTD A2–3 grade (moderate to severe hydronephrosis) by antenatal evaluation. After birth, all of the 24 infants (70.6%) with UTD A1 grade had normal ultrasonic findings of urinary tract; while the other 10 cases with UTD A2–3 grade had persistent abnormalities of urinary tract by postnatal assessment, sorted as UTD P1 grade (mild hydronephrosis) in 6 cases (17.6%), UTD P2 grade (moderate hydronephrosis) in 2 cases (5.9%) and UTD P3 grade (severe hydronephrosis) in 2 cases (5.9%). The most common postnatal urological abnormality of isolated fetal hydronephrosis was vesicoureteral reflux. During the follow-up period, 7 infants (20.6%) had urinary tract infection episodes and very few obtained positive cultures of the urine. Only 2 infants (5.9%) with the diagnosis of ureterovesical junction obstruction required surgery intervention, who were both classified as UTD P3 grade. None of the children with UTD P1 and P2 grades needed operation. The UTD classification system described the urinary tract both antenatally and postnatally, which could point out the correlation between fetal hydronephrosis and postnatal urological abnormalities. This new classification system is expected to be a good prognostic marker for fetal hydronephrosis.