Due to the increased use of prenatal imaging, UPJ obstruction may be identified before any symptoms are present. If any dilation (hydronephrosis) is identified, the baby will be monitored throughout the pregnancy and after birth. Once the baby is born further imaging studies may confirm the obstruction. Older children may experience back or flank pain. The pain may be associated with nausea and vomiting. Other symptoms might include bloody urine, a urinary tract infection (often with a fever), or might even be a vague abdominal pain.