Hydronephrosis in pregnancy is common in the second and third trimester. Only a few cases are symptomatic, caused by a ureteric stone or by the pregnancy itself. The clinical dilemma is when to treat and when not to treat. We propose a multidisciplinary management based on renal ultrasonography to verify hydronephrosis and renography to diagnose obstructive hydronephrosis. Obstruction with a high intra-renal pressure must be treated to avoid kidney dysfunction. Patients with pyonephrosis need immediate treatment.