Optimal timing of initial postnatal ultrasonography in newborns with prenatal hydronephrosis

Conflicting data exist concerning optimal timing for initial postnatal ultrasound in newborns with prenatal hydronephrosis. To determine whether timing significantly affects the accuracy of postnatal ultrasound, we conducted a prospective study comparing ultrasound within 48 hours of birth and at 7 to 10 days of life.

A total of 21 consecutive newborns with prenatal hydronephrosis were enrolled in 14 months. Prenatal hydronephrosis was defined as a pelvic diameter 4 mm. or greater before 33 weeks and 8 mm. or greater beginning at 33 weeks of gestation. Postnatal hydronephrosis was assessed using the Society for Fetal Urology grading system. Patients were subsequently followed with serial ultrasound and adjunctive imaging studies.

Of the 32 evaluable renal units a majority had a change in the degree of hydronephrosis between the first and second ultrasound. An increase in hydronephrosis was found in 14 (44%) renal units with an increase of 2 or greater grades in 8 (25%). At a median followup of 15 months only 3 renal units had a persistent increase in hydronephrosis. None had greater than grade 2 hydronephrosis or required therapeutic intervention. A decrease in hydronephrosis between the first and second ultrasound was noted in 8 (25%) renal units. Seven renal units were excluded from analysis due to unequivocal obstruction, and none of these demonstrated a change between the 2 sonograms.

The degree of hydronephrosis varied between scans performed in the first 48 hours and 7 to 10 days of life in most newborns. The initial ultrasound more commonly underestimated the degree of hydronephrosis but this difference was not clinically significant at further followup. We recommend initial postnatal sonogram at 7 to 10 days of life for routine prenatal hydronephrosis but earlier scans may be appropriate in select cases.