Prenatal diagnosis of urinary tract anomalies. The value of two ultrasound examinations.

OBJECTIVE: To determine when fetal urinary tract anomalies were detected by ultrasound screening during pregnancy and to discuss the possible consequences if only one early ultrasound examination is performed. DESIGN: A retrospective study of 47 cases where fetal urinary tract malformations were diagnosed in a two-stage screening program (17th and 32nd week of gestation) covering 22,310 women over ten years, 1982-91. SETTING: Ullevål University Hospital in Oslo which serves as a referral center for obstetric and neonatal diseases. RESULTS: Urinary tract anomalies were diagnosed in 0.18% of the pregnancies. Of these, 61.7% were found at the second routine ultrasound screening. The most difficult differential diagnoses were those of hydronephrosis without megaureter and a multicystic kidney. Hydronephrosis was found in 51% and a multicystic kidney in 21% of the cases. The tentative prenatal diagnoses were confirmed postnatally in 83% of the cases. Six of the fetuses had anomalies regarded as incompatible with postnatal life. These pregnancies were terminated, and the diagnoses verified by autopsy. Two other infants died perinatally, one of them as a result of the urinary tract anomalies. CONCLUSION: If only one ultrasound scanning had been performed in the 17th week, approximately two-thirds of the cases would not have been detected. Early intervention and follow-up after delivery would only have been performed if the infants had developed symptoms or complications related to the urinary tract anomalies.