title: Hydronephrosis index: a better physiological reference in antenatal ultrasound for assessment of fetal hydronephrosis.
abstract: OBJECTIVE
  To establish a nomogram of fetal hydronephrosis index (HI) (anteroposterior diameter of renal pelvis divided by urinary bladder volume) at different gestational ages, to serve as a new reference for antenatal ultrasound examination, and to avoid overestimation of fetal hydronephrosis due to transient effect of a distended fetal bladder.
  
  
  METHODS
  504 uncomplicated singleton pregnancies from 20 to 38 weeks' gestation were included. In each fetus, the maximum anteroposterior diameters of both renal pelves were measured on transverse view of fetal kidneys. Urinary bladder volume was calculated using the ovoid volume formula. HI was derived accordingly.
  
  
  RESULTS
  Values of HI vary significantly at different trimesters of pregnancy. HI was much higher (mean = 0.1543) from 20 to 27 weeks' gestation, and its value decreased significantly (mean = 0.0253) from 28 to 38 weeks' gestation (P < .05, independent-sample t test). As gestational age increased, HI decreased (R(2) = 0.5921).
  
  
  CONCLUSIONS
  HI is easy to be measured and can be used as a new physiological reference for assessment of fetal hydronephrosis by eliminating the confounding effect of a full fetal bladder. The change in values of HI throughout gestation supports the clinical importance of a nomogram for this new index.
authors.affiliation: Diagnostic Radiology and Organ Imaging Department, Prince of Wales Hospital, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong SAR, China.
authors.forename: Vivian Yee-fong
authors.initials: VY
authors.lastname: Leung
authors.forename: Winnie Chiu-wing
authors.initials: WC
authors.lastname: Chu
authors.forename: Constantine
authors.initials: C
authors.lastname: Metreweli
mesh_terms: D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging*; D005865:Gestational Age; D006801:Humans; D006869:Hydronephrosis / Q000000981:diagnostic imaging*; D007682:Kidney Pelvis / Q000000981:diagnostic imaging / Q000196:embryology; D049451:Nomograms; D011247:Pregnancy; D016216:Ultrasonography, Prenatal; D001743:Urinary Bladder / Q000000981:diagnostic imaging / Q000196:embryology