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New formulas for calculating the lung-to-head ratio in healthy fetuses between 20 and 40 weeks' gestation
Sven Kehl1, Sven Eckert, Sebastian Berlit
1Department of Obstetrics and Gynecology, University Medical Center Mannheim, Heidelberg University, Theodor-Kutzer-Ufer 1-3, 68167 Mannheim, Germany. sven.kehl@gmail.com.
Objectives:
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.
