Sonographic characteristics of the urinary tract in healthy neonates

In infancy it has been reported that intravesical pressure is generally higher in males than in females. We investigated whether there are significant differences in the sonographic characteristics of the urinary tract in male and female neonates.

The study comprised 280 consecutive full-term newborns, including 146 males and 134 females. Kidneys were assessed for hydronephrosis and graded according to Society for Fetal Urology guidelines. Kidney measurements included maximum longitudinal length and largest longitudinal area. Bladder measurements included bladder dimensions and wall thickness. Bladder wall thickness was measured only in neonates with an estimated bladder volume of greater than 10 ml.

Of the 280 neonates 114 had mild renal pelvic dilatation in at least 1 kidney and the incidence in males was significantly higher than in females (53% versus 27%). Kidney longitudinal length and largest area were significantly greater in males on each side. Mean bladder volume was essentially equal in the 169 male and female neonates with an estimated bladder volume of greater than 10 ml. but mean bladder wall thickness was significantly greater in males than in females (1.63 versus 1.38 mm.).

Our study shows that there are marked differences in sonographic findings in male and female neonates in regard to renal pelvic dilatation, renal size and bladder wall thickness. These differences should be considered when sonography is done for screening for urinary tract anomalies in newborns.