title: Facial profile markers in second- and third-trimester fetuses with trisomy 18.
abstract: OBJECTIVE
  To evaluate nasal bone length (NBL), maxilla-nasion-mandible (MNM) angle, fetal profile (FP) line, prenasal thickness (PT), prenasal thickness to nasal bone length (PT:NBL) ratio and prefrontal space ratio (PFSR) as markers of trisomy 18 in the second and third trimesters of pregnancy.
  
  
  METHODS
  The NBL, MNM angle, FP line, PT, PT:NBL ratio and PFSR were measured retrospectively from stored two-dimensional images or three-dimensional volumes of trisomy-18 fetuses, and were compared with our previously reported normal ranges for euploid fetuses. Additional ultrasound findings were noted at initial routine second-trimester scan and at subsequent advanced ultrasound examination performed after referral for karyotyping.
  
  
  RESULTS
  A total of 43 trisomy-18 fetuses were included in the analysis. At initial examination, median gestational age was 21 + 2 weeks. NBL and PT were correlated with gestational age (P < 0.001), but the other markers were not. Mean NBL, MNM angle, PT, PT:NBL ratio and PFSR were 3.76 mm, 16.67°, 4.25 mm, 1.39 and 0.87, respectively. The FP line was zero (normal) in 53.7% of cases and negative (abnormal) in 46.3%. All markers were significantly associated with trisomy 18, with the PT:NBL ratio yielding the highest detection rate (88.4%) followed by NBL (83.7%), MNM angle (56.4%), FP line (46.3%), PT (27.9%) and the PFSR (20.5%) (for a 5% false-positive rate for the continuous variables). Various combinations of the four best markers (NBL, FP line, MNM angle and PT:NBL ratio) yielded detection rates of between 72% and 95%. Structural anomalies were not detected in 22% of fetuses at the initial scan and in 2% at the advanced scan.
  
  
  CONCLUSIONS
  The PT:NBL ratio and NBL are robust second- and third-trimester markers for trisomy 18. A negative FP line has a 0% false-positive rate and the potential to differentiate between trisomy 18 and Down syndrome, as in the latter the FP line is often positive. No major anomaly was observed at the initial scan in about a quarter of trisomy-18 fetuses, underlining the role of second-trimester facial marker evaluation.
authors.affiliation: Fetal Medicine Unit, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: F I
authors.initials: FI
authors.lastname: Vos
authors.affiliation: Department of Obstetrics and Gynecology, St Antonius Hospital, Nieuwegein, The Netherlands.
authors.forename: E A P
authors.initials: EA
authors.lastname: de Jong-Pleij
authors.affiliation: Fetal Medicine Unit, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: Bakker
authors.affiliation: Department of Statistics, St Antonius Hospital, Nieuwegein, The Netherlands.
authors.forename: E
authors.initials: E
authors.lastname: Tromp
authors.affiliation: Fetal Medicine Unit, University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: G T R
authors.initials: GT
authors.lastname: Manten
authors.affiliation: Fetal Medicine Unit, University Medical Centre Groningen, University of Groningen, Groningen, The Netherlands.
authors.forename: C M
authors.initials: CM
authors.lastname: Bilardo
mesh_terms: D016022:Case-Control Studies; D002887:Chromosomes, Human, Pair 18 / Q000000981:diagnostic imaging; D005145:Face / Q000002:abnormalities / Q000000981:diagnostic imaging*; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods; D009295:Nasal Bone / Q000002:abnormalities / Q000000981:diagnostic imaging*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012189:Retrospective Studies; D014314:Trisomy; D000073842:Trisomy 18 Syndrome; D016216:Ultrasonography, Prenatal / Q000379:methods
keywords: fetal profile line; maxilla-nasion-mandible angle; nasal bone length, prefrontal space ratio; prenasal thickness; prenasal thickness-nasal bone length ratio; trisomy 18