Antenatal hydronephrosis: infants with minor postnatal dilatation do not need prophylaxis.

The aim of this study was to determine the occurrence of urinary tract infection (UTI) in infants with antenatal renal pelvis dilatation (ARPD). Consecutive ultrasound (US) screening of 14,000 pregnant women detected ARPD >or=5 mm in 106 foetuses. After birth, two US examinations were performed: on the fifth to seventh day and during the third week of life. The findings were considered normal when renal pelvis dilatation (RPD) was <or=7 mm on both examinations and no other signs of abnormality were present. Voiding cystourethrography (VCUG) was done in all infants 6-8 weeks after birth. One hundred and three infants were followed for 2 years. Antibacterial prophylaxis (trimethoprim 1 mg/kg per day) was given to those with RPD >or=15 mm, vesicoureteric reflux (VUR) grades III-V and suspected obstruction. In 53/103 babies, both US examinations were normal, three had VUR grade I. Two girls had UTI at 18 and 24 months of age, respectively. Among the 50 infants with abnormal initial US, six had VUR, of which four were high grade (IV-V). All four developed UTI. We conclude that UTI is uncommon in infants with two normal postnatal US examinations. Routine use of antibacterial prophylaxis in these infants therefore cannot be recommended.