Antenatal Hydronephrosis

Early detection of many fetal abnormalities is now possible due to the availability of antenatal ultrasound screening in the 12th to 16th week of gestation. Regarding urinary tract anomalies, most can be detected at 18–20 weeks of gestation. The incidence of antenatal hydronephrosis is 0.6–4.5%, and it makes up about 92% of antenatally-detected urinary tract anomalies. If antenatal hydronephrosis is detected, the patient should be carefully followed-up in order to identify the associated congenital anomaly. Usually, if the renal pelvic diameter exceeds 5 mm in the second trimester, then fetal ultrasonography should be repeated in the third trimester. Renal pelvic diameter greater then 7 mm is often related to a significant congenital anomaly; therefore, a plan for management after birth should be detailed. The newborn should be treated with prophylactic antibiotics and investigative imaging studies should be arranged accordingly.