*2.10.2. Observed/expected lung-to-head ratio*

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 [31, 32].

O/E LHR = (observed LHR/expected LHR) × 100

There has been proposed a four-step stratification of fetuses based on their observed/expected (O/E) LHR wherein it was also taken into account their liver position.



**Table 7.** Key points.

<sup>•</sup> Prenatal prediction of postnatal outcome in CDH patients is based on ultrasound measurement of contralateral lung size and magnetic resonance total lung volumetry.
