The quantitative lung index (QLI): a gestational age-independent sonographic predictor of fetal lung growth

OBJECTIVE: We sought to develop a gestational age-independent sonographic parameter to characterize lung growth. STUDY DESIGN: Reported descriptors of lung growth, including lung-to-head circumference (HC) ratio (LHR) and observed/expected LHR, were examined. A new index, the quantitative lung index (QLI) was derived using published data on HC and the area of the base of the right lung. RESULTS: Neither the LHR nor the observed/expected LHR proved to be gestational age independent. Right lung growth can be expressed using the following formula: QLI = lung area/(HC/10)(boolean AND)2. The 50th percentile of the QLI remained constant at approximately 1.0 for the gestational age between 16-32 weeks. A small lung (< 1st percentile) was defined as a QLI < 0.6. CONCLUSION: Fetal right lung growth can be adequately described using the QLI, independent of gestational age. Further studies are needed to assess the clinical accuracy of the QLI in characterizing fetal right lung growth.