title: Natural history of fetal hydronephrosis diagnosed on mid-trimester ultrasound.
abstract: OBJECTIVE
  Renal tract dilatation is a common finding in routine prenatal ultrasound. However, there is no consensus as to the criteria used for differentiating pathological from physiological dilatation. The aim of this study was to evaluate the natural history and postnatal outcome of fetal hydronephrosis in an unselected obstetric population.
  
  
  METHODS
  This was a prospective study of fetal hydronephrosis, detected at 18-23 weeks' gestation, in a routine obstetric population. Fetal hydronephrosis was diagnosed as 'mild' if the antero-posterior renal pelvic diameter (APRPD) measured >or = 4 mm and as 'moderate/severe' if the APRPD measured > or = 7 mm or if there was associated calyceal dilatation. The postnatal outcome of fetuses with persistent hydronephrosis (> or = 10 mm in the third trimester) was determined from a postal questionnaire.
  
  
  RESULTS
  During the study period, 11 465 women underwent an anomaly scan at 18-23 weeks of gestation. Fetal hydronephrosis was identified in 2.3% (268/11 465) of women. Mild hydronephrosis was present in 80.6% (216/268) and moderate/severe hydronephrosis in 19.4% (52/268). The hydronephrosis resolved in the antenatal or early neonatal period in 88% of fetuses. None of the fetuses with mild hydronephrosis and approximately one in three fetuses with persistent moderate/severe hydronephrosis required postnatal surgery. Overall, only one in every 1000 total births in the study population required postnatal urological surgery.
  
  
  CONCLUSIONS
  The current study highlights the natural history of antenatally detected hydronephrosis. Mild fetal hydronephrosis appears to be associated with an excellent prognosis and probably represents the group with physiological renal pelvic dilatation. Moderate/severe fetal hydronephrosis is associated with poorer outcome and is perhaps the group that will need more intense follow up both antenatally and postnatally.
authors: Feto-Maternal Medicine Unit, Homerton Hospital, Academic Unit of Obstetrics and Gynaecology, St Bartholomew's and The Royal London School of Medicine and Dentistry, London, UK.
authors: S
authors: S
authors: Sairam
authors: A
authors: A
authors: Al-Habib
authors: S
authors: S
authors: Sasson
authors: B
authors: B
authors: Thilaganathan
mesh_terms: D000328:Adult; D005260:Female; D005315:Fetal Diseases / Q000000981:diagnostic imaging* / Q000503:physiopathology; D006801:Humans; D006869:Hydronephrosis / Q000000981:diagnostic imaging* / Q000503:physiopathology / Q000601:surgery; D011247:Pregnancy; D011256:Pregnancy Outcome; D011262:Pregnancy Trimester, Second; D011379:Prognosis; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal