Background The neonatal period has been characterized as a time when males have a much higher incidence of urinary infection and severe ureteral reflux than females. However, little information about the voiding function in the neonatal period is available.
Methods. The bladder urine volumes, before and after voiding, and urinary how rates were determined with the use of noninvasive voiding-provocation maneuvers and ultrasound in the apparently normal neonates.
Results. There was no significant difference in the prevoid bladder urine volume between the two sexes. After they were stimulated to enhance the tension of their abdominal wall musculature, 65 of 118 females (55.1%) and 64 of 115 males (55.7%) voided. The voiding was observed in 94 (81.0%) of the 116 neonates who had had a prevoid volume above 12 ml. The residual urine expressed as a percentage of the prevoid volume was significantly higher in the males (median, 12.0% in males vs. 3.0% in females, P < 0.01), with the values being above 20% in 26 (41%) of the 64 males compared with 10 (15%) of the 65 females (P < 0.01). Urinary flow rates, determined in 52 neonates, were significantly smaller in males than in females (mean +/- so, 2.6 +/- 0.9 g/second vs. 3.8 +/- 1.3 g/second, respectively, P < 0.001).
Conclusion. This voiding function study with ultrasound using noninvasive voiding-provocation maneuvers successfully revealed that male neonates have a larger residual urine volume and smaller urinary flow rates than female neonates. This study should be useful for the diagnosis of voiding dysfunction in children with abnormal urinary symptoms.