Perinatology.com logo

perinatology.com

Lung area to Head circumference Ratio (LHR), o/e LHR, and Quantitative Lung Index (QLI)

LHR, o/e LHR, and bilateral QLI calculator

Use for fetal thoracic lesions when the contralateral lung area and/or individual right and left lung areas are measured.

Measurements are entered in millimeters and mm², matching the legacy LHR calculator. QLI remains valid when area and HC use consistent units. Measurement help, formulas, illustrations, cautions, and references are collapsed for mobile use.

Show measurement instructions and images

Measurement instructions

  1. Image plane: use a transverse fetal thoracic image at the four-chamber view.
  2. LHR / o/e LHR: measure the lung contralateral to the CDH or dominant thoracic lesion.
  3. Longest-diameter method: measure the longest diameter of the contralateral lung and the longest perpendicular diameter; the calculator multiplies Length 1 × Length 2.
  4. Tracing method: trace the border of the contralateral lung and enter the traced area. If the matching QLI field is blank, this traced area is automatically reused for the contralateral QLI.
  5. QLI-R and QLI-L: trace the right lung and/or left lung separately. The calculator labels which one is contralateral after you select lesion side.
  6. HC: enter fetal head circumference in the same unit system used by the legacy calculator, usually millimeters.

Longest-diameter LHR method

LHR measurement using two longest perpendicular diameters of the contralateral fetal lung at the four-chamber view
Use the lung opposite the lesion for LHR/o/e LHR. Enter Length 1 and Length 2 in millimeters.

Tracing method for LHR and QLI

LHR tracing method showing traced contralateral fetal lung area at the four-chamber view
Trace the visible lung area. Enter traced area in mm². For QLI, right- and left-lung areas may be entered separately.
1. Select fetal thoracic lesion side

Contralateral lung area for LHR / o/e LHR

Longest diameter method

Lung area = Length 1 × Length 2.

Tracing method

Also used automatically for contralateral QLI if the matching QLI lung-area field is blank.
Manual tracing is generally more reproducible than the longest-diameter method.

QLI lung areas

When to enter right and left QLI areas

For CPAM/fetal lung lesions, enter the right and/or left lung traced area at the four-chamber view. The output labels each lung as contralateral or ipsilateral based on lesion side.

Fetal size and gestational age

1 cm² = 100 mm²
Calculation methods

Calculation methods

MetricCalculationUse
LHRObserved LHR = lung area / HCUses contralateral lung area, either longest-diameter area or traced area.
o/e LHRo/e LHR = observed LHR / expected LHR × 100Uses expected LHR equations for lesion side, gestational age, and measurement method.
QLI-RRight lung area / (HC/10)²Right lung fetal-size-normalized area; small-lung threshold used here: <0.6.
QLI-LLeft lung area / (HC/12)²Left lung fetal-size-normalized area from the CPAM calculator workflow; small-lung threshold used here: <0.5.

Because the legacy calculator uses mm and mm², QLI is calculated directly from mm² and mm. The same formulas also work with cm² and cm when units are internally consistent.

Measurement illustrations

Measurement illustrations

These use the original Perinatology.com measurement illustrations rather than embedded SVG drawings.

Longest-diameter LHR method

LHR longest-diameter method at the fetal four-chamber view
Use the product of the two longest perpendicular diameters of the contralateral lung for the longest-diameter LHR method.

Tracing method

LHR traced-area method at the fetal four-chamber view
Use manual tracing of the lung boundary for the traced-area LHR method. The same traced lung-area concept is used for QLI-R and QLI-L.
Laterality instruction: for a left-sided lesion, the right lung is contralateral and QLI-R is the contralateral QLI. For a right-sided lesion, the left lung is contralateral and QLI-L is the contralateral QLI. For bilateral or complex lesions, interpret QLI-R and QLI-L separately.
QLI interpretation

QLI interpretation

The Quantitative Lung Index was proposed as a gestational-age-independent sonographic measure of fetal lung growth. In the right-lung QLI paper, the median was approximately 1.0 from 16–32 weeks and a small lung was defined as QLI <0.6. The CPAM calculator also included the left-lung modification, using QLI-L = left lung area / (HC/12)², with a proposed small-lung threshold of <0.5.

For a left-sided lesion the contralateral lung is right, so QLI-R is the contralateral QLI. For a right-sided lesion the contralateral lung is left, so QLI-L is the contralateral QLI. For bilateral or complex lesions, interpret both separately.

Clinical cautions

Clinical cautions

  • LHR and o/e LHR are primarily CDH-derived risk tools; avoid applying historical CDH prognostic cutoffs as direct CPAM delivery or ECMO directives.
  • For CPAM or other lung lesions, QLI should be interpreted alongside CVR, mediastinal shift/mass effect, hydrops, lesion type, growth trend, and local fetal/neonatal protocols.
  • Manual tracing is generally preferred when feasible because the longest-diameter method can overestimate lung area compared with tracing.
Expected LHR equations retained from legacy calculator

Expected LHR equations retained from legacy calculator

Show equations

Longest diameter method

Expected right LHR in left-sided CDH/lesion: -3.4802 + 0.3995 × GA - 0.0048 × GA² (Jani); -3.480 + 0.399 × GA - 0.004 × GA² (Dekoninck).

Expected left LHR in right-sided CDH/lesion: -2.5957 + 0.3043 × GA - 0.0042 × GA² (Jani).

Tracing method

Expected right LHR in left-sided CDH/lesion: -2.2481 + 0.2712 × GA - 0.0033 × GA² (Peralta); -2.3271 + 0.27 × GA - 0.0032 × GA² (Jani); -2.356 + 0.272 × GA - 0.003 × GA² (Dekoninck).

Expected left LHR in right-sided CDH/lesion: -1.4815 + 0.1824 × GA - 0.0023 × GA² (Peralta); -1.4994 + 0.1778 × GA - 0.0021 × GA² (Jani).

GA = gestational age in weeks.

References

References

Show full reference list
  1. 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;32:1634-1636. PMID: 9396544.
  2. Alfaraj MA, et al. Congenital diaphragmatic hernia: lung-to-head ratio and lung volume for prediction of outcome. Am J Obstet Gynecol. 2011;205:43.e1-8. PMID: 21529758.
  3. Quintero RA, et al. The quantitative lung index: a gestational age-independent sonographic predictor of fetal lung growth. Am J Obstet Gynecol. 2011;205:544.e1-8. DOI: 10.1016/j.ajog.2011.07.031.
  4. Kontopoulos EV, et al. The quantitative lung index: the left lung. J Matern Fetal Neonatal Med. 2022;35:4142-4148. DOI: 10.1080/14767058.2020.1847076.
  5. Metkus AP, et al. Sonographic predictors of survival in fetal diaphragmatic hernia. J Pediatr Surg. 1996;31:148-151. PMID: 8632269.
  6. Peralta CFA, et al. Assessment of lung area in normal fetuses at 12-32 weeks. Ultrasound Obstet Gynecol. 2005;26:718-724. PMID: 16308896.
  7. Jani J, et al. Observed to expected lung area to head circumference ratio in the prediction of survival in fetuses with isolated diaphragmatic hernia. Ultrasound Obstet Gynecol. 2007;30:67-71. PMID: 17587219.
  8. Jani JC, et al. Lung-to-head ratio: a need to unify the technique. Ultrasound Obstet Gynecol. 2012;39:2-6. DOI: 10.1002/uog.11065.
  9. 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;87:619-624. DOI: 10.1016/j.earlhumdev.2011.08.001.
  10. Crombleholme TM, et al. Cystic adenomatoid malformation volume ratio predicts outcome in prenatally diagnosed cystic adenomatoid malformation of the lung. J Pediatr Surg. 2002;37:331-338. PMID: 11877643.
  11. Peters NCJ, et al. Prediction of postnatal outcome in fetuses with congenital lung malformation: 2-year follow-up study. Ultrasound Obstet Gynecol. 2021;58:428-438. DOI: 10.1002/uog.23542.