title: Visualisation and measurement of tracheal diameter in the sheep fetus: an ultrasound study with stereomicroscopic correlation.
abstract: OBJECTIVE
  There is no information on ultrasonographic visualisation of the upper airways in the sheep fetus, but this species permits to examine the accuracy of ultrasonography in measuring the inner tracheal diameter. This was the aim of our study.
  
  
  METHODS
  Transabdominal ultrasonography to visualise the trachea was attempted in 16 unsedated Welsh Mountain ewes with a singleton pregnancy at 70 (SD 2) days gestation (term 148 days). The ultrasonographically measured inner tracheal diameter was compared with the actual inner tracheal diameter obtained by stereomicroscopy post-mortem.
  
  
  RESULTS
  High-resolution ultrasonography permitted clear imaging of the fetal trachea in 87% (14/16) of the cases analysed. The ultrasound measurements were smaller than the corresponding stereomicroscopic measurements, the mean +/- SD difference between the measurements being 0.40 +/- 0.12 mm.
  
  
  CONCLUSIONS
  Improvements in ultrasound have led to increased interest in the assessment of the trachea in human fetuses. Our study in the ovine fetus at mid gestation shows that optimal views of the fetal trachea allowing accurate measurements can be obtained in almost all the cases.
authors.affiliation: Fetal and Neonatal Research Group, Department of Obstetrics and Gynaecology, University College London Medical School, London, UK. karim.kalache@charite.de
authors.forename: K D
authors.initials: KD
authors.lastname: Kalache
authors.forename: H
authors.initials: H
authors.lastname: Nishina
authors.forename: D
authors.initials: D
authors.lastname: Ojutiku
authors.forename: M A
authors.initials: MA
authors.lastname: Hanson
mesh_terms: D000818:Animals; D005260:Female; D008853:Microscopy / Q000379:methods; D011247:Pregnancy; D012756:Sheep; D014132:Trachea / Q000000981:diagnostic imaging / Q000196:embryology*; D016216:Ultrasonography, Prenatal