Ultrasound screening for fetal urinary tract malformations: a prospective study in general population.

Routine ultrasound examination at a first level ultrasound unit was performed on 4586 fetuses in general pregnant population at 18 and 34 weeks, to detect urinary tract malformations. Suspected renal abnormality was confirmed by postnatal investigations. Infants were followed up to 2-4 years to detect any renal malformations missed in screening. Urinary tract abnormalities were observed antenatally in 27 fetuses, eight cases at 18 weeks, and 19 cases at 34 weeks. An anteroposterior diameter of renal pelvis of 1 cm or more was the criterion for fetal hydronephrosis, which was the main ultrasound finding in 18 fetuses showing 24 hydronephrotic kidneys. In five cases, slight hydronephrosis disappeared spontaneously after birth, explaining the five 'false positive' cases of the study. Four children had renal abnormalities that were missed antenatally. The incidence of true urinary tract malformations detected by screening antenatally was 0.48%, and the overall incidence after 2-4 years follow-up was 0.57%, which is much higher than reported earlier in series without routine ultrasound screening. The antenatal screening showed a sensitivity of 84.6%, a specificity of 99.9%, a positive predictive value of 81.5%, and a negative predictive value of 99.9%. The main differential diagnostic problems occurred in two fields: in differentiating (1) functional hydronephrosis from obstructive uropathy, and (2) multicystic renal dysplasia of Potter's type IV from severe hydronephrosis. The prenatal diagnosis in cases with definitive renal abnormality corresponded to the postnatal diagnosis in 19/22 (86.4%) of the cases. 68% of the infants with urinary tract anomaly survived, 60% of them undergoing postnatal surgery.(ABSTRACT TRUNCATED AT 250 WORDS)