title: Normal ranges of fetal nasal bone length during the second trimester in an Iranian population.
abstract: OBJECTIVE
  To provide a normal reference range for nasal bone length (NBL) during the second trimester of pregnancy in an Iranian population.
  
  
  METHODS
  This cross-sectional study was performed on 3201 fetuses at 15 to 28 weeks of gestational age (GA). Both singleton and twin fetuses were evaluated. The relationship between NBL and GA was determined and percentile values for each gestational week were provided.
  
  
  RESULTS
  NBL measurement was obtained in 98% of singleton and 96% of twin fetuses. There was a linear relationship between GA and NBL both in singleton (R(2) = 0.62) and in twin (R(2) = 0.74) fetuses. There was no significant difference between twins regarding NBL (p = 0.18).
  
  
  CONCLUSIONS
  We have provided the normal reference range for NBL during the second trimester in an Iranian population. NBL in singleton and twin fetuses is similar and there is no significant difference between twins regarding NBL.
authors.affiliation: Maternal Fetal Medicine Department, Tehran University of Medical Sciences, Tehran, Iran.
authors.forename: Fatemeh
authors.initials: F
authors.lastname: Rahimi-Sharbaf
authors.forename: Ahmad-Reza
authors.initials: AR
authors.lastname: Tahmasebpour
authors.forename: Reihaneh
authors.initials: R
authors.lastname: Pirjani
authors.forename: Saeed Reza
authors.initials: SR
authors.lastname: Ghaffari
authors.forename: Abbas
authors.initials: A
authors.lastname: Rahimi-Foroushani
mesh_terms: D001837:Body Weights and Measures; D003430:Cross-Sectional Studies; D005260:Female; D005865:Gestational Age; D057238:Growth Charts; D006801:Humans; D007492:Iran; D009295:Nasal Bone / Q000000981:diagnostic imaging / Q000196:embryology / Q000254:growth & development*; D049451:Nomograms; D011153:Population; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000208:ethnology / Q000502:physiology; D011272:Pregnancy, Multiple / Q000208:ethnology / Q000706:statistics & numerical data; D014427:Twins; D016216:Ultrasonography, Prenatal / Q000592:standards / Q000706:statistics & numerical data