title: First trimester risk assessment for trisomy 21 in twin pregnancies combining nuchal translucency and first trimester biochemical markers.
abstract: OBJECTIVE
  The aim is to describe the performance of first-trimester combined risk assessment in twin pregnancies.
  
  
  METHODS
  Maternal serum free beta-human chorionic gonadotrophin and pregnancy-associated plasma protein A (PAPP-A) were determined at 8 to 12 weeks and fetal nuchal translucency (NT) was measured at 11 to 13+6 weeks. The individual risk was estimated for each fetus using the combined test in dichorionic twins. In monochorionic twins, the mean risk assessment of the two fetuses was used. An invasive diagnostic procedure was offered when the risk was ≥ 1 : 270 in either one of the fetuses.
  
  
  RESULTS
  From February 2007 to June 2011, 447 twin pregnancies were enrolled in this study. There were 402 (89.9%) dichorionic and 45 (10.1%) monochorionic twins. In dichorionic twins, mean crown-rump length (CRL) was 63.9 mm; median NT multiples of the median (MoM) was 0.97; median Β-hCG was MoM 1.74; median PAPP-A was 1.72. In monochorionic twins, mean CRL was 61.9 mm; median NT MoM was 0. 98; median Β-hCG MoM was 1.44; and median PAPP-A was 1.51. Two pregnancies with Down syndrome were detected by first trimester screening, both in dichorionic twins. The false positive rate was 5.7% (95% confidence interval 4.1-7.3) and 4.4% (95% confidence interval 0.1-8.8%) in dichorionic and monochorionic twins, respectively.
  
  
  CONCLUSIONS
  The combined test in twins appears to be a good method for Down syndrome screening with a high detection rate and an acceptable false-positive rate.
authors: Fetal Medicine Service, Department of Obstetrics, Gynecology and Reproductive Medicine, Institut Universitari Dexeus, Barcelona, Spain. pilpra@dexeus.com
authors: Pilar
authors: P
authors: Prats
authors: Ignacio
authors: I
authors: Rodríguez
authors: Carmina
authors: C
authors: Comas
authors: Bienvenido
authors: B
authors: Puerto
mesh_terms: D000328:Adult; D015415:Biomarkers / Q000097:blood*; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D018568:Crown-Rump Length; D004200:Diseases in Twins / Q000175:diagnosis*; D004314:Down Syndrome / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D005865:Gestational Age; D006801:Humans; D008423:Maternal Age; D008875:Middle Aged; D048208:Nuchal Translucency Measurement; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D059285:Pregnancy, Twin; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011296:Prenatal Diagnosis / Q000379:methods*; D018570:Risk Assessment
chemical_list: D015415:Biomarkers; D018997:Chorionic Gonadotropin, beta Subunit, Human; D011266:Pregnancy-Associated Plasma Protein-A