LHR, o/e LHR, and QLI calculator
The calculator below may be used to estimate the LHR, the o/e LHR, and the QLI.
Quintero and colleagues have proposed, that mathematically, neither the LHR nor the observed/expected LHR are gestational age independent and should therefore be used with caution in predicting neonatal outcome. (3)
The Lung area to Head circumference Ratio (LHR)
The lung-to-head circumference ratio (LHR) is a sonographic measure proposed to identify fetuses with congenital diaphragmatic hernia (CDH) that have a poor prognosis (4).
The lung area contralateral to the CDH was originally obtained by taking the product of the longest two perpendicular linear measurements of the lung measured at the level of the 4-chamber view of the heart on a transverse scan of the fetal thorax. The product is divided by the head circumference (HC) to obtain the LHR.
Lung area = Length 1 × Length 2
The Lung area to Head circumference Ratio (LHR) = Lung area / Head circumference
In a cross-sectional study of 650 normal singleton pregnancies Peralta and associates (5) found manual tracing of the lung to be a more reproducible way of measuring the lung area. In addition, the longest diameter method overestimated the right and left lung areas by about 45% compared to the tracing method.
Using the tracing method the lung area contralateral to the CDH is obtained by tracing of the limits of the lung.
The Lung area to Head circumference Ratio (LHR) = Lung area / Head circumference
Observed/expected lung-to-head ratio (o/e LHR)
Peralta and associates (5,7) also found that the left and right LHR increased exponentially with gestation. Because the LHR is not gestational age independent, as previously assumed, Jani and colleagues (6) proposed the introduction of a new measurement, the observed to expected (o/e) LHR, to correct for gestational age.
The observed LHR may be expressed as a percentage of the expected mean for gestational age as the Observed/expected lung-to-head ratio (o/e LHR) (6,9).
o/e LHR = (Observed LHR / Expected LHR) × 100
Where the Expected LHR using Longest Diameter Method is
Expected Right LHR in left CDH
= –3.4802 + (0.3995 × GA) – (0.0048 × GA²) (Jani)
= –3.480 + (0.399 × GA) – (0.004 × GA²) (Dekoninck)
Expected Left LHR in right CDH
= –2.5957 + (0.3043 × GA) – (0.0042 × GA²) (Jani)
GA = gestational age in weeks
Where the Expected LHR using the Tracing Method is
Expected Right LHR in left CDH
–2.2481 + (0.2712 × GA) – (0.0033 × GA²) (Peralta 2005)
–2.3271 + (0.27 × GA) – (0.0032 × GA²) (Jani)
–2.356 + (0.272 × GA) – (0.003 × GA²) (Dekoninck)
Expected Left LHR in right CDH
–1.4815 + (0.1824 × GA) – (0.0023 × GA²) (Peralta 2005)
–1.4994 + (0.1778 × GA) – (0.0021 × GA²) (Jani)
GA = gestational age in weeks
The Quantitative Lung Index (QLI)
Quintero and colleagues (3) proposed, mathematically, that neither the LHR nor the observed/expected LHR are gestational age independent. They derived a new parameter to describe right lung growth, expressed as the quantitative lung index (QLI) = lung area / (HC / 10)². The 50th percentile of the QLI is constant at approximately 1.0 for the gestational age between 16–32 weeks. They defined a small lung (<1st percentile) as a QLI < 0.6. Further studies are needed to assess the merits of this new parameter.
Acknowledgements
We would like to express our very great appreciation to Dr Ramen Chmait, director of the CHLA-USC Fetal Therapy Program for his valuable and constructive suggestions in the development of this calculator.
References
- Lipshutz GS, et al. Prospective analysis of lung-to-head ratio predicts survival for patients with prenatally diagnosed congenital diaphragmatic hernia. J Pediatr Surg. 1997 Nov;32(11):1634–6. PMID: 9396544
- Alfaraj MA, et al. Congenital diaphragmatic hernia: lung-to-head ratio and lung volume for prediction of outcome. Am J Obstet Gynecol. 2011 Jul;205(1):43.e1–8. PMID: 21529758
- Quintero RA, et al. The quantitative lung index (QLI): a gestational age-independent sonographic predictor of fetal lung growth. Am J Obstet Gynecol. 2011 Dec;205(6):544.e1–8. Epub 2011 Jul 22. PMID: 21944224
- Metkus AP, et al. Sonographic predictors of survival in fetal diaphragmatic hernia. J Pediatr Surg. 1996 Jan;31(1):148–51. PMID: 8632269
- Peralta CF, et al. Assessment of lung area in normal fetuses at 12–32 weeks. Ultrasound Obstet Gynecol. 2005 Dec;26(7):718–24. PMID: 16308896
- Jani J, et al. Observed to expected lung area to head circumference ratio in the prediction of survival in fetuses with isolated diaphragmatic hernia. Antenatal-CDH-Registry Group. Ultrasound Obstet Gynecol. 2007 Jul;30(1):67–71. PMID: 17587219
- Peralta CF, et al. Left and right lung volumes in fetuses with diaphragmatic hernia. Ultrasound Obstet Gynecol. 2006 May;27(5):551–4. PMID: 1658647
- Jani JC, et al. Lung-to-head ratio: a need to unify the technique. Ultrasound Obstet Gynecol. 2012 Jan;39(1):2–6. doi:10.1002/uog.11065. PMID: 22213615
- Dekoninck P, et al. Results of fetal endoscopic tracheal occlusion for congenital diaphragmatic hernia and the set up of the randomized controlled TOTAL trial. Early Hum Dev. 2011 Sep;87(9):619–24. doi:10.1016/j.earlhumdev.2011.08.001.
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