The characteristics of primary vesico‐ureteric reflux in male and female infants with pre‐natal hydronephrosis

Objective  To examine the characteristics of primary vesico‐ureteric reflux (VUR) in young infants following prenatal hydronephrosis. Patients and methods  The study comprised 155 consecutive infants with VUR detected at a mean age of 8.7 weeks (sd 6.3). Reflux units ( n =236) were analysed for relationships between gender, severity of reflux, exposure to urinary tract infection (UTI) and the presence of focal and generalized types of kidney damage on imaging. Bladder wall thickness (from ultrasonography) was examined in comparison with a further group of 29 males without VUR. Results  Male infants predominated (117 of 155, 75%); bilateral VUR affected the same proportion (52%) of males and females. Most kidneys exposed to VUR (158 of 236, 67%) were normal and of the 78 abnormal kidneys (57 without UTI), 53 showed generalized damage (only eight exposed to UTI) and 71 (91%) were associated with severe (grades IV and V) reflux that predominantly affected males ( P <0.001). Grade V reflux was almost exclusively a male disorder. Most female units (45 of 58, 78%) compared with 46% (82/178) of male units had mild (grades I to III) reflux that was independently associated with normal kidneys. The mean bladder wall thickness was significantly greater for males with VUR than for females with VUR and for males without VUR. Conclusions  Two distinct but not exclusive patterns of VUR were identified: (i) mild reflux associated with normal kidneys that affected most females and a proportion of males; (ii) severe reflux combined with kidney damage, most likely fetal in origin, that is almost exclusively a male disorder.