title: Normative values of fetal nasal bone lengths of Turkish singleton pregnancies in the first trimester.
abstract: OBJECTIVE
  Evaluation of nasal bone improves the performance of first-trimester screening for trisomy 21. In this retrospective study we aimed to determine normative values related to the measurement of nasal bone length of the Turkish population during the first trimester ultrasonographic fetal screening.
  
  
  METHODS
  Medical records of singleton pregnancies, whose first trimester fetal screening was performed between 2004 and 2010, were evaluated retrospectively. Pregnancies with any detected/suspicious anatomical or genetic fetal anomalies, biochemical abnormalities, increased nuchal translucency measurements, and pregnancies of artificial reproduction techniques were excluded from data analyses. Mean±standard deviation, median and percentile values of the length of nasal bone were calculated separately for 11(0-6), 12(0-6) and 13(0-6) gestational weeks.
  
  
  RESULTS
  Nasal bone could be visualized in 99.6% of the included 1762 singleton pregnancies. In 16.5% of the cases nasal bones were only noted as present or absent. Mean maternal age was 29.67±4.50 years and mean gestational age was 12.54±0.61 weeks. Median values of nasal bone lengths were 1.7, 1.9, and 2.2 mm for 11(0-6), 12(0-6) and 13(0-6) gestational weeks respectively. Nasal bone length (NBL) increased linearly with advancing gestational age and CRL. NBL (mm)=[0.298xGestational Age (week)]-1.779, R(2)=0.318; p<0.001; NBL (mm)= [0.023 × CRL (mm)] + 0.520, R(2)=0.331; p<0.001.
  
  
  CONCLUSIONS
  The present study presents normative values of nasal bone in the first trimester screening of normal singleton pregnancies of Turkish population. Nasal bone length increases with advancing gestational age and CRL.
authors.affiliation: Department of Gynecology and Obstetrics, International Hospital, İstanbul, Turkey.
authors.forename: Murat
authors.initials: M
authors.lastname: Yayla
authors.affiliation: Department of Gynecology and Obstetrics, Bayındır Hospital İçerenköy, İstanbul, Turkey.
authors.forename: Rahime Nida
authors.initials: RN
authors.lastname: Ergin
authors.affiliation: Department of Gynecology and Obstetrics, Göztepe Education and Research Hospital, İstanbul, Turkey.
authors.forename: Gökhan
authors.initials: G
authors.lastname: Göynümer
keywords: Screening; fetus; nasal bone; pregnancy; ultrasonography