New formulae for calculating Lung-to-Head-Ratio in normal fetuses between 20 and 40 weeks of gestation

Purpose: In prenatal management of fetuses with congenital diaphragmatic hernia (CDH), the prediction of the likely outcome relies on indirect assessment of fetal lung volume. Herefore, the sonographic measurement of the fetal lung area to head circumference ratio (LHR) is used. The observed to expected LHR (o/e LHR) was introduced to eliminate the gestational effect. To calculate the o/e LHR the measured LHR should be divided by the expected mean LHR for gestational age. The expected mean LHR is calculated using formulae that were developed in a study with an inappropriate population. For this, the aim of this…