Antenatal Hydronephrosis

Objectives: To describe the maternal and fetal characteristics of isolated antenatal hydronephrosis (ANH), to address parental concerns by providing local data based on the fetal renal pelvis anteroposterior diameter (APD), and to determine the most effective APD cutoff in the second and third trimester for prediction of postnatal urological outcome. Methods: A retrospective review of all cases referred to the prenatal diagnostic clinic over a 21-month period from 1 January 2013 to 30 September 2014 was performed. All the 4010 ultrasound examination reports were retrieved and those diagnostic of ANH were identified. Antenatal hydronephrosis was defined by the system based on the APD proposed by the Society for Fetal Urology. Maternal and fetal characteristics were studied. Postnatal uropathy and surgery were the events of interest. Results: Overall, 90.8% of kidneys with isolated ANH detected in the third trimester were found to have normal anatomy after birth. Of the 153 fetuses studied, eight were identified to have postnatal uropathy of whom four underwent surgical intervention. Fetuses with second-trimester APD of >10 mm were at increased risk of postnatal uropathy (odds ratio=10.35; 95% confidence interval, 1.80-59.60; p=0.01), whereas third-trimester APD of ≥9 mm also demonstrated a significant risk (odds ratio=8.56; 95% confidence interval, 1.03-71.30; p=0.04). Third-trimester APD better predicted both postnatal uropathy and need for surgical intervention than second-trimester APD (p≤0.001). The respective best cutoff above which postnatal uropathy and surgery was anticipated were 7.3 mm and 9.6 mm in the third trimester (sensitivity 75% and specificity 76.7% for postnatal uropathy, 100% and 93.3% for surgery). Conclusion: Fetal renal pelvis APD, particularly when measured during the third trimester, serves as a good predictor of postnatal uropathy and need for surgical intervention. Measurement of the APD remains the most important factor in predicting fetal urological outcome. Hong Kong J Gynaecol Obstet Midwifery 2016; 16(1):29-38