Voiding function study with ultrasound in male and female neonates

Background The neonatal period has been characterized as a time when males have a much higher incidence of urinary infection and severe ureteral reflu x than females. However, little information about the voiding function in t he neonatal period is available. Methods. The bladder urine volumes, before and after voiding, and urinary h ow rates were determined with the use of noninvasive voiding-provocation ma neuvers and ultrasound in the apparently normal neonates. Results. There was no significant difference in the prevoid bladder urine v olume between the two sexes. After they were stimulated to enhance the tens ion of their abdominal wall musculature, 65 of 118 females (55.1%) and 64 o f 115 males (55.7%) voided. The voiding was observed in 94 (81.0%) of the 1 16 neonates who had had a prevoid volume above 12 ml. The residual urine ex pressed as a percentage of the prevoid volume was significantly higher in t he males (median, 12.0% in males vs. 3.0% in females, P < 0.01), with the v alues 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 v oiding-provocation maneuvers successfully revealed that male neonates have a larger residual urine volume and smaller urinary flow rates than female n eonates. This study should be useful for the diagnosis of voiding dysfuncti on in children with abnormal urinary symptoms.