title: Isolated fetal pyelectasis and chromosomal abnormalities.
abstract: OBJECTIVE
  The primary objective of this study was to determine if isolated pyelectasis is a risk factor for trisomy 21.
  
  
  METHODS
  Twelve thousand, six hundred and seventy-two unselected singleton fetuses were examined by prenatal ultrasound during the second trimester at a single institution. The sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio of pyelectasis (either isolated or in association with other soft markers/structural anomalies) to detect trisomy 21 were calculated.
  
  
  RESULTS
  Pyelectasis (anteroposterior pelvic diameter >/=4 mm) was detected in 2.9% (366/12,672) of the fetuses. Among these, 83.3% (305/366) were isolated, and 16.7% (61/366) were associated with other markers/structural anomalies. The prevalence of trisomy 21 was 0.087% (11/12,672) and, among these fetuses, 2 (18.1%) had pyelectasis, 1 isolated, and 1 associated with other markers/structural anomalies. The presence of isolated pyelectasis had 9.09% sensitivity, 97.6% specificity, 0.33% positive predictive value, and 99.9% negative predictive value to detect fetuses with trisomy 21. The likelihood ratio of trisomy 21 in this group of fetuses was 3.79 (95% CI 0.582-24.616). Among fetuses with pyelectasis and other associated markers/structural anomalies, the sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio for trisomy 21 were 9.09%, 99.5%, 1.64%, 99.9%, and 19.2 (95% CI 2.91-126.44).
  
  
  CONCLUSIONS
  In the absence of other findings, isolated pyelectasis is not a justification for the performance of an amniocentesis.
authors.affiliation: Department of Ultrasound, Women's Health Alliance, Nashville, TN, USA. cl.coco@vodafone.it
authors.forename: Claudio
authors.initials: C
authors.lastname: Coco
authors.forename: Philippe
authors.initials: P
authors.lastname: Jeanty
mesh_terms: D004108:Dilatation, Pathologic; D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000453:epidemiology*; D005260:Female; D005333:Fetus / Q000473:pathology*; D006801:Humans; D007682:Kidney Pelvis / Q000000981:diagnostic imaging / Q000196:embryology / Q000473:pathology*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal