title: Screening for aneuploidy in first and second trimesters: is there an optimal paradigm?
abstract: OBJECTIVE
  This review serves to explore the recent literature regarding aneuploidy screening in both first and second trimesters. We aim to construct a comparative analysis of a range of proposed strategies for screening for trisomy 21.
  
  
  RESULTS
  First trimester combined screening (sonographic nuchal translucency combined with serum markers pregnancy-associated plasma protein A and the free beta subunit of human chorionic gonadotrophin) has superseded second trimester serum screening (alpha-fetoprotein, total human chorionic gonadotrophin, unconjugated estriol with or without inhibin-A) as a screening paradigm for the detection of trisomy 21. This move is attributed to the recognition of superior detection rates, lower false-positive rates and earlier results associated with the former strategy. Septated cystic hygroma has been recognized as a distinct entity which confers a high risk of aneuploidy and structural malformations. Further advances in screening performance are achievable by combining the results of first and second-trimester screens in a sequential manner, with much interest generated by programs that only include second-trimester testing contingent upon first-trimester results.
  
  
  CONCLUSIONS
  Screening strategies for aneuploidy continue to evolve, with the most recent evidence favouring a contingent sequential approach.
authors.affiliation: Department of Obstetrics and Gynaecology, Royal College of Surgeons in Ireland, Rotunda Hospital, Dublin, Ireland.
authors.forename: Fionnuala M
authors.initials: FM
authors.lastname: Breathnach
authors.forename: Fergal D
authors.initials: FD
authors.lastname: Malone
mesh_terms: D000782:Aneuploidy; D015415:Biomarkers; D005260:Female; D005315:Fetal Diseases / Q000097:blood / Q000000981:diagnostic imaging; D006801:Humans; D048208:Nuchal Translucency Measurement / Q000379:methods*; D011247:Pregnancy; D011261:Pregnancy Trimester, First; D011262:Pregnancy Trimester, Second; D011296:Prenatal Diagnosis / Q000379:methods*; D012680:Sensitivity and Specificity
chemical_list: D015415:Biomarkers