title: First-trimester Down syndrome screening in renal-transplanted pregnant women: a model for adjusting the false-positives rates.
abstract: OBJECTIVE
  This study aimed to develop a model to adjust the increased β-hCG levels observed in renal-transplanted women, leading to increased false-positive rates in Down syndrome screening.
  
  
  METHODS
  Detailed data from 11 renal-transplanted and a nested-cohort of 70 pregnant women, matched by age, parity and gestational age were retrieved from our hospital records. Patient's age, multiples of the median (MoM) values for freeβ-hCG, pregnancy-associated plasma protein-A, nuchal translucency, and creatinine concentration and clearance were noted. Freeβ-hCG levels were adjusted according to the deviation of serum creatinine concentration by means of three different methods (median, proportionality and regression). Subsequently, Down syndrome risk was estimated with the three resulting adjusted fβ-hCG values.
  
  
  RESULTS
  After adjustment, the median β-hCG MoM decreased from 2.15 MoM to 1.00 MoM (median method), 1.61 MoM (proportionality method) or 1.16 MoM (regression method). The non-adjusted 27% false-positive rate dropped to 18% (median method) and 10% (proportionality or regression methods) after re-estimation of the Down syndrome risk. In controls, the observed median for β-hCG MoM was 1.12, and the false-positive rate was 5.7%.
  
  
  CONCLUSIONS
  In first-trimester Down syndrome screening, fβ-hCG adjustment by the regression method appears to be the best to match with controls.
authors.affiliation: Department of Maternal-Fetal Medicine, Institute Gynecology, Obstetrics and Neonatology, Hospital Clínic, Barcelona Catalonia, Spain.
authors.forename: Maribel
authors.initials: M
authors.lastname: Grande
authors.forename: Vicenç
authors.initials: V
authors.lastname: Cararach
authors.forename: Elena
authors.initials: E
authors.lastname: Casals
authors.forename: Antoni
authors.initials: A
authors.lastname: Borrell
mesh_terms: D000328:Adult; D016022:Case-Control Studies; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood; D003404:Creatinine / Q000097:blood / Q000493:pharmacokinetics / Q000652:urine; D004314:Down Syndrome / Q000175:diagnosis*; D005189:False Positive Reactions; D005260:Female; D006801:Humans; D007674:Kidney Diseases / Q000097:blood* / Q000534:rehabilitation / Q000628:therapy / Q000652:urine; D016030:Kidney Transplantation; D008657:Metabolic Clearance Rate / Q000502:physiology; D008954:Models, Biological; D011247:Pregnancy; D011248:Pregnancy Complications / Q000097:blood* / Q000378:metabolism / Q000652:urine; D011261:Pregnancy Trimester, First / Q000097:blood*; D011266:Pregnancy-Associated Plasma Protein-A / Q000032:analysis; D011296:Prenatal Diagnosis / Q000379:methods*; D012189:Retrospective Studies
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D003404:Creatinine; D011266:Pregnancy-Associated Plasma Protein-A