title: Systematic review of screening for trisomy 21 in twin pregnancies in first trimester combining nuchal translucency and biochemical markers: a meta-analysis.
abstract: OBJECTIVE
  This article is a systematic review of the literature to establish the detection rate and false-positive rate of the combined test for the screening of trisomy 21 in twins.
  
  
  METHODS
  We conducted a literature search (MEDLINE, EMBASE and ScienceDirect and Cochrane) to identify studies between 1995 and 2013 that provided data on the combined test in twins. Selected studies included data on maternal age, number of fetuses affected by Down syndrome, test strategy, sensitivity and specificity of the test.
  
  
  RESULTS
  The combined test in twins had a pooled sensitivity of 0.893 [95% confidence interval (CI) 0.797-0.947] and a pooled specificity of 0.946 (95% CI 0.933-0.957). The performance of the test was good (summary receiver operating characteristic area under the curve: 0.817). In dichorionic twins, sensitivity and specificity were 0.862 (95% CI 0.728-0.936) and 0.952 (95% CI 0.942-0.96), respectively. In monochorionic twins, the sensitivity and specificity were 0.874% (95% CI 0.526-0.977) and 0.954% (95% CI 0.943-0.963), respectively.
  
  
  CONCLUSIONS
  The results of this meta-analysis show that the accumulative evidence on the performance of the combined test in twin pregnancies is good. Nowadays, it seems to be the best first-trimester screening test available for twin pregnancies.
authors.affiliation: Fetal Medicine Service, Department of Obstetrics, Gynecology and Reproductive Medicine, Hospital Universitari Quirón Dexeus, Barcelona, Spain.
authors.forename: Pilar
authors.initials: P
authors.lastname: Prats
authors.forename: Ignacio
authors.initials: I
authors.lastname: Rodríguez
authors.forename: Carmina
authors.initials: C
authors.lastname: Comas
authors.forename: Bienvenido
authors.initials: B
authors.lastname: Puerto
mesh_terms: D015415:Biomarkers / Q000097:blood*; D004200:Diseases in Twins / Q000097:blood / Q000175:diagnosis* / Q000453:epidemiology; D004314:Down Syndrome / Q000175:diagnosis* / Q000453:epidemiology; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First / Q000097:blood; D059285:Pregnancy, Twin / Q000097:blood / Q000706:statistics & numerical data; D011296:Prenatal Diagnosis / Q000379:methods; D014427:Twins
chemical_list: D015415:Biomarkers