title: Normative data for fetal cisterna magna length measurement between 18 and 24 weeks of pregnancy.
abstract: OBJECTIVE
  The aim of this study was to determine normative data for fetal cisterna magna length (CML) measurement in a Brazilian population.
  
  
  METHODS
  This was a retrospective cross-sectional study on 3,862 normal singleton pregnancies between the 18th and 24th weeks of pregnancy. Fetal CML was measured in the axial plane of the fetal head, at lateral ventricle level, including the cavum septum pellucidum, thalamus, third ventricle, and transverse cerebellar diameter. The anteroposterior measurement was made between the posterior border of the cerebellar vermis and the internal face of the occipital bone. To assess the correlation between CML and gestational age (GA), polynomial equations were calculated, with adjustments using determination coefficient (R2).
  
  
  RESULTS
  The mean CML ranged from 4.29±0.93 mm at 18 to 18+6 weeks to 5.58±1.23 mm at 24 to 24+6 weeks of pregnancy. There was a good correlation between CML and GA, best represented by a linear equation: CML=0.535+0.208*GA (R2=0.084).
  
  
  CONCLUSIONS
  We established normative data for fetal CML in the second trimester of pregnancy, in a large Brazilian population.
authors.forename: Edward
authors.initials: E
authors.lastname: Araujo Júnior
authors.forename: Wellington P
authors.initials: WP
authors.lastname: Martins
authors.forename: Liliam Cristine
authors.initials: LC
authors.lastname: Rolo
authors.forename: Claudio Rodrigues
authors.initials: CR
authors.lastname: Pires
authors.forename: Sebastião Marques
authors.initials: SM
authors.lastname: Zanforlin Filho
mesh_terms: D000328:Adult; D002946:Cisterna Magna / Q000000981:diagnostic imaging* / Q000196:embryology*; D003430:Cross-Sectional Studies; D016208:Databases, Factual / Q000639:trends; D005260:Female; D005333:Fetus / Q000196:embryology; D005865:Gestational Age; D006801:Humans; D011247:Pregnancy; D011262:Pregnancy Trimester, Second / Q000502:physiology; D012016:Reference Values; D012189:Retrospective Studies; D016216:Ultrasonography, Prenatal / Q000639:trends*; D055815:Young Adult