The quantitative lung index: the left lung

Abstract

Objective: We have previously described a gestational age-independent sonographic parameter to assess fetal lung growth in the right lung (right quantitative lung index, or QLI-R). The purpose of this study was to develop a similar sonographic parameter to assess the growth of the left lung in the fetus, independent of gestational age, or QLI-L.

Study design: A new index, the QLI-L was derived using published formulas for the head circumference (HC) and the area of the base of the left lung (LA), with the corresponding percentiles.

Results: Left lung growth can be expressed using the following formula: $\mathrm{QLI}-L=\frac{{\mathrm{LA}}_L}{{\left(\frac{\mathrm{HC}}{12}\right)}^2}.$ The 50th percentile of the QLI-L remained approximately constant at 1.0 for the GA between 16-32 weeks. A small left lung (<1st percentile) was defined as a QLI-L < 0.5.

Conclusions: Fetal left lung growth can be adequately described independent of gestational age using the QLI-L. Further experience is needed to assess the clinical accuracy of the QLI-L in characterizing fetal left lung growth.

Keywords: Quantitative lung index; congenital diaphragmatic hernia; lung-to-head ratio; tracheal occlusion.