Free voiding patterns in preterm and full-term newborn infants are different between males and females

The neonatal period is critical in bladder development, encompassing the transition from foetal bladder contractions to voluntary infant urination. The aim of this study was to investigate different voiding parameters between male and female newborn infants.

We studied 102 healthy, single birth newborn infants - 54 preterm and 48 full-term - without lower urinary tract diseases, hospitalised in the neonatal intensive care unit from March 2011 to March 2012. Free voiding was observed from 9 a.m. to 9 p.m., and the free voiding parameters and fluid intake were recorded and compared between male and female newborn infants using the Student's t-test and chi-square test.

Male preterm newborns demonstrated larger mean postvoid residual volumes and lower bladder emptying rates than female preterm newborns (p < 0.05), and male full-term newborns had lower bladder emptying rates than female full-term newborns (p < 0.05). The bladder emptying rates of newborns defecating simultaneously with voiding were not statistically different between males and females of the same gestational age (p > 0.05).

Male newborns were more likely to have larger postvoid residual volumes than females, and defecating simultaneously with voiding may promote bladder emptying in male newborns.