Predicting Neonatal Deaths and Pulmonary Hypoplasia in Isolated Congenital Diaphragmatic Hernia Using the Sonographic Fetal Lung Volume-Body Weight Ratio

Rodrigo Ruano; Marie-Cecile Aubry; Yves Dumez; Marcelo Zugaib; Alexandra Benachi

Disclosures

Am J Roentgenol. 2008;190(5):1216-1219. 

In This Article

Abstract and Introduction

Objective: The objective of our study was to evaluate the potential of the sonographic fetal lung volume–body weight ratio to predict neonatal deaths and pulmonary hypoplasia in fetuses with isolated congenital diaphragmatic hernia (CDH).
Subjects and Methods: Between January 2002 and December 2004, 40 fetuses with isolated CDH and 450 control subjects were prospectively evaluated in two centers. Fetal lung volumes were estimated on 3D sonography using the rotational technique and fetal weight on 2D sonography using the Hadlock equation. The ratio of sonographic fetal lung volume to body weight was calculated in each case and was correlated with neonatal deaths using the Mann-Whitney U test. Accuracies of the ratio in predicting neonatal deaths and pathologic diagnosis of pulmonary hypoplasia were also evaluated.
Results: The ratio of sonographic fetal lung volume to body weight is constant throughout gestation, with a mean value of 0.025. The ratio was significantly lower in neonates that died (median, 0.009; range, 0.004–0.021) than in those that survived (median, 0.011; range, 0.008–0.020) (p = 0.018). Pulmonary hypoplasia was suspected prenatally in 34 of 40 (85.0%) fetuses with CDH, in all cases of death (100%), and in seven of nine (77.8%) neonates that survived. At autopsy, pulmonary hypoplasia was diagnosed in 19 cases (86.4%). Accuracies of the ratio in predicting neonatal deaths and pulmonary hypoplasia were 64.5% (20/31) and 86.4% (19/22), respectively.
Conclusion: The sonographic fetal lung volume–body weight ratio can be used more accurately to diagnose pulmonary hypoplasia than to predict neonatal deaths in fetuses with isolated CDH. Further studies are necessary to show the prevalence of pulmonary hypoplasia in fetuses with isolated CDH and its importance for predicting neonatal deaths.

Congenital diaphragmatic hernia (CDH) occurs in approximately 1 in 2,200 live births, with an overall neonatal mortality rate of 50% in prenatally diagnosed cases.[1] Prenatal prediction of neonatal prognosis remains a challenge.[2,3] Because neonatal mortality is directly related to severe pulmonary hypoplasia, many prognostic factors based on prenatal assessment of lung size (fetal lung volumes and lung-over-head ratio) have been suggested.[4,5,6,7,8,9] Many authors have used a relative lung volume ratio, in which the observed lung volume is compared with the expected value for each specific gestational age, and have reported that a ratio of observed fetal lung volume to expected fetal lung volume of less than 0.35 is associated with poorer outcome.[7,8]

Tanigaki et al.[10] proposed that the ratio of fetal lung volume estimated on MRI and fetal body weight estimated on sonography be used for the prediction of pulmonary hypoplasia. These authors' suggestion is based on the pathologic definition of pulmonary hypoplasia: a ratio of lung weight to body weight of <0.012 at a gestational age of 28 weeks and of <0.015 at <28 weeks.[11,12,13,14] In that study,[10] a high accuracy (88%) of this method in predicting pulmonary hypoplasia was observed. Other investigators have shown that fetal lung volumes can be measured precisely using 3D sonography in CDH cases with results similar to MRI estimates of lung volume[7,8,15] and to postmortem fetal lung weights.[16] Ruano et al.[17] also reported that the fetal lung volume–body weight ratio can be measured by combining 3D sonography and 2D sonography with good accuracy when compared with postmortem examinations.

On the basis of these findings, we prospectively studied the potential of the sonographic fetal lung volume–body weight ratio to predict neonatal deaths and pulmonary hypoplasia in 40 fetuses with isolated CDH, after evaluating the distribution of the ratio against gestational age in 450 healthy control subjects.

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