Normative values of fetal nasal bone lengths of Turkish singleton pregnancies in the first trimester [Türk Tekil Gebeliklerdeki Fetal Nazal Kemik Uzunluklari{dotless}ni{dotless}n Birinci Trimester Normal Deǧerleri]

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. material and 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 110-6,120-6 and 130-6 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 110-6,120-6 and 130-6 gestational weeks respectively. nasal bone length (nbl) increased linearly with advancing gestational age and crl. nbl (mm)=[0.298xgestational age (week)]-1.779,r2=0.318; p<0.001; nbl (mm)= [0.023 x crl (mm)] + 0.520,r2=0.331; p<0.001 conclusion: 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. © copyright 2011 by the turkish-german gynecological education and research foundation.