title: New formulas for calculating the lung-to-head ratio in healthy fetuses between 20 and 40 weeks' gestation.
abstract: OBJECTIVE
  The purpose of this study was to develop new formulas for the expected fetal lung area-to-head circumference ratio in normal singleton pregnancies between 20 and 40 weeks' gestation.
  
  
  METHODS
  The lung-to-head ratio and complete fetal biometric parameters of 126 fetuses between 20 and 40 weeks' gestation were prospectively measured. The lung-to-head ratio was measured by 3 different methods (longest diameter, anteroposterior diameter, and tracing). Formulas for predicting right and left lung-to-head ratios with regard to gestational age and biometric parameters were derived by stepwise regression analysis.
  
  
  RESULTS
  New formulas for calculating right and left lung-to-head ratios by each measurement method were derived. The formulas included gestational age only and no biometric parameters.
  
  
  CONCLUSIONS
  The new formulas for estimating the expected lung-to-head ratio by the 3 different methods in normal singleton pregnancies up to 40 weeks' gestation may help improve the prognostic power of observed-to-expected lung-to-head ratio assessment in fetuses with congenital diaphragmatic hernias.
authors.affiliation: Department of Obstetrics and Gynecology, University Medical Center Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany. sven.kehl@gmail.com.
authors.forename: Sven
authors.initials: S
authors.lastname: Kehl
authors.forename: Sven
authors.initials: S
authors.lastname: Eckert
authors.forename: Sebastian
authors.initials: S
authors.lastname: Berlit
authors.forename: Benjamin
authors.initials: B
authors.lastname: Tuschy
authors.forename: Marc
authors.initials: M
authors.lastname: Sütterlin
authors.forename: Jörn
authors.initials: J
authors.lastname: Siemer
mesh_terms: D000465:Algorithms; D000886:Anthropometry / Q000379:methods; D005260:Female; D006257:Head / Q000000981:diagnostic imaging* / Q000196:embryology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D008168:Lung / Q000000981:diagnostic imaging* / Q000196:embryology*; D008297:Male; D011247:Pregnancy; D011262:Pregnancy Trimester, Second; D011263:Pregnancy Trimester, Third; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods*
keywords: anteroposterior method; expected lung-to-head ratio; formulas; longest diameter method; lung-to-head ratio; tracing method