Management of Antenatal Hydronephrosis

Abstract

An abnormality of the urinary tract is identified in 1–2% of pregnancies, depending on the sonographic criteria. The most common abnormality is pyelectasis or hydronephrosis. At 20 weeks gestation, an anterior-posterior renal pelvic diameter (APRPD) <4 mm is normal and at 32 weeks an APRPD < 7 mm is normal. Renal abnormalities are more common in the third trimester, when the fetal urine output is higher. A multidisciplinary consensus conference established criteria for assigning risk to both antenatal and postnatal hydronephrosis using the urinary tract dilation (UTD) system. In utero, ultrasound (US) is beneficial in recognizing abnormalities of the fetal urinary tract but usually, definitive diagnosis is delayed until postnatal evaluation is performed. In the fetus with bilateral hydronephrosis and oligohydramnios, renal cortical cysts, hypertonic fetal urine, and elevated fetal urinary beta 2-microglobulin are unfavorable prognostic indices. In most fetuses with antenatal hydronephrosis, postnatal imaging is delayed for 96 h because of neonatal oliguria, which might underestimate the severity of hydronephrosis. Overall, approximately 10% ultimately undergo surgical intervention, 70% have nonobstructive hydronephrosis and undergo serial US until the hydronephrosis resolves and 20% undergo more extensive imaging and continue to be followed without intervention.