title: Gender-related fetal development of the internal urethral sphincter.
abstract: OBJECTIVE
  To investigate the fetal development of the internal urethral sphincter and the gender-related morphologic differences of the bladder outlet.
  
  
  METHODS
  Thirty-seven (14 female, 23 male) fetal bladder neck specimens (mean gestational age, 19.4 weeks) with the smooth muscle complex of the internal sphincter were investigated histologically. After immunostaining serial sections in 3 reference planes (sagittal, frontal, and horizontal) of the bladder neck, the internal sphincter volumes and bladder outlet diameters were measured and correlated with gender and age of gestation.
  
  
  RESULTS
  Between the 18th and 40th week of gestation, an exponential growth of the internal sphincter muscle with significant higher volumes could be observed in male fetuses compared with female fetuses (internal sphincter volumes, P = .006; radius of the sphincter complex, P = .001). As a result of this gender difference, the bladder outlet was significantly (P = .001) narrower in male than in female fetuses. Moreover, we found a significant positive correlation between age and all measured parameters in both male and female specimens.
  
  
  CONCLUSIONS
  The present study indicates a significant closer bladder outlet in male fetuses compared than in females. It thereby provides evidence of a gender-related functional obstruction in addition to a suppositious transient infravesical obstruction in male human fetuses.
authors.affiliation: Department of Pediatric Urology, St. Vincent' s Hospital, Linz, Austria. Electronic address: josef.oswald@bhs.at.
authors.forename: Josef
authors.initials: J
authors.lastname: Oswald
authors.forename: Isabel
authors.initials: I
authors.lastname: Heidegger
authors.forename: Eberhard
authors.initials: E
authors.lastname: Steiner
authors.forename: Erich
authors.initials: E
authors.lastname: Brenner
authors.forename: Michael
authors.initials: M
authors.lastname: Ladurner Rennau
authors.forename: Renate
authors.initials: R
authors.lastname: Pichler
authors.forename: Tanja
authors.initials: T
authors.lastname: Becker
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Loidl
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Horninger
authors.forename: Helga
authors.initials: H
authors.lastname: Fritsch
mesh_terms: D005260:Female; D047109:Fetal Development; D005865:Gestational Age; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D012737:Sex Factors; D014521:Urethra / Q000033:anatomy & histology / Q000196:embryology*; D001743:Urinary Bladder / Q000196:embryology*