title: Isolated fetal pyelectasis and the risk of Down syndrome: a meta-analysis.
abstract: OBJECTIVE
  We performed a meta-analysis to examine the performance of second-trimester (14-24 weeks' gestation) isolated fetal pyelectasis as a marker for trisomy 21 and to calculate its associated weighted pooled likelihood ratios.
  
  
  METHODS
  PubMed, Ovid MEDLINE and Cochrane databases were searched using the terms 'pyelectasis' and 'pelviectasis'. Studies were included if fetuses with isolated pyelectasis were reported separately from fetuses with other soft markers of aneuploidy and/or structural anomalies and if knowledge of the fetal karyotype was unknown at the time of ultrasound examination.
  
  
  RESULTS
  Individual study statistics were pooled as weighted positive and negative likelihood ratios with 95% CIs, using a random-effects model. Ten observational studies were included (2148 cases of isolated pyelectasis). Isolated fetal pyelectasis was defined in seven out of 10 studies as a renal pelvis anteroposterior diameter of ≥ 4 mm. Isolated fetal pyelectasis was associated with pooled positive and negative likelihood ratios of 2.78 (95% CI, 1.75-4.43) and 0.99 (95% CI, 0.98-1.00), respectively.
  
  
  CONCLUSIONS
  The detection of isolated fetal pyelectasis on mid-trimester ultrasound is associated with an increased likelihood of trisomy 21. If the finding of isolated fetal pyelectasis is used to adjust the trisomy 21 risk from maternal serum screening tests, a positive likelihood ratio of 2.78 should be used in the calculation.
authors.affiliation: Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Thomas Jefferson University, Philadelphia, PA, USA.
authors.forename: K M
authors.initials: KM
authors.lastname: Orzechowski
authors.forename: V
authors.initials: V
authors.lastname: Berghella
mesh_terms: D004314:Down Syndrome / Q000453:epidemiology*; D005260:Female; D006801:Humans; D007682:Kidney Pelvis / Q000000981:diagnostic imaging; D016013:Likelihood Functions; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D058536:Pyelectasis / Q000000981:diagnostic imaging / Q000453:epidemiology*; D012306:Risk; D016216:Ultrasonography, Prenatal
keywords: isolated fetal pyelectasis; prenatal diagnosis; risk adjustment; trisomy 21