title: Suspicious Prenasal Skin Thickness-to-Nasal Bone Length Ratio: Prevalence and Correlation with Other Markers in Second and Third Trimester Fetuses with Down Syndrome.
abstract: OBJECTIVE
  To assess the prevalence and value of a suspicious prenasal skin thickness-to-nasal bone length ratio (PT/NB ratio) in comparison to other established markers in a large population of Down syndrome (DS) fetuses.
  
  
  METHODS
  This was a retrospective study of 139 DS fetuses and 530 normal fetuses scanned after 14 + 0 weeks of gestation. To characterize diagnostic performance, we used the ROC curve approach. The presence or absence of a PT/NB ratio > 0.8 and 11 other markers were assessed in the group of DS fetuses. A correlation analysis was performed in order to investigate associations between PT/NB ratio and other markers.
  
  
  RESULTS
  Among DS fetuses the median PT/NB ratio was 1.06 (IQR 0.729) and was significantly higher compared to normal fetuses with 0.62 (IQR 0.148), (p < 0.001). Gestational age had no influence on the PT/NB ratio. A PT/NB ratio > 0.8 had the highest prevalence of all markers with 89.2 % in the group of DS fetuses, 3 cases were negative for all markers and 3 cases were positive only for PT/NB ratio > 0.8. Marker-specific comparison between prevalences of a suspicious PT/NB ratio with respect to the presence or absence of other markers was statistically significant for hypoplastic NB and major anomalies (p < 0.05). Utilization of at least one of the following five markers was sufficient for detecting 136 out of 139 fetuses with trisomy 21: suspicious PT/NB ratio, hypoplastic NB, nuchal fold thickness, white spot, shortened femur.
  
  
  CONCLUSIONS
  The PT/NB ratio is one of the most powerful indicators of DS in the second trimester. It is objective to interpret, easy to measure, and is reproducible.
authors.affiliation: Obstetrics and Gynecology, Center for Prenatal Diagnosis and Human Genetics Kudamm-199, Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Hagen
authors.affiliation: Obstetrics and Gynecology, Center for Prenatal Diagnosis and Human Genetics Kudamm-199, Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Albig
authors.affiliation: Statistik, ACOMED, Leipzig, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Keller
authors.affiliation: Human Genetics, Center for Prenatal Diagnosis and Human Genetics Kudamm-199, Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Stumm
authors.affiliation: Obstetrics and Gynecology, Center for Prenatal Diagnosis and Human Genetics Kudamm-199, Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Entezami
mesh_terms: D004314:Down Syndrome / Q000000981:diagnostic imaging* / Q000196:embryology*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D009295:Nasal Bone / Q000000981:diagnostic imaging* / Q000196:embryology*; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012372:ROC Curve; D012016:Reference Values; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D012867:Skin / Q000000981:diagnostic imaging* / Q000196:embryology*; D013223:Statistics as Topic; D016216:Ultrasonography, Prenatal / Q000379:methods*