Lung Size Measurement in Left‐Sided Congenital Diaphragmatic Hernia: Does Position of the Fetus Affect Results?

Objective To compare the difference in lung size measurement in fetuses with left‐sided congenital diaphragmatic hernia (L‐CDH) by means of the observed/expected lung‐to‐head ratio (O/E‐LHR) in two different fetal positions. Method Prospective cohort of L‐CDH fetuses, with O/E‐LHR measurements by one experienced investigator but with the fetus in two positions: with the contralateral lung close and one with the lung away from the ultrasound probe. A Bland‐Altman analysis was performed to assess the agreement between lung measurements in both fetal positions. Results 49 L‐CDH fetuses underwent paired assessments of lung size at a mean gestational age of 28.8 (17.7–37.7) weeks. Lung size estimation with the lung distant to the probe consistently underestimates the O/E‐LHR values compared to measurements obtained using the lung close to the probe. On average, O/E‐LHR values were 11.3% (95% confidence intervals (CI), 7.5%–15.0%) higher when the lung was close to the probe. When the lung was distant to the probe, a higher proportion of CDH fetuses were classified in a more severe group than when it was evaluated close to the probe ( p < 0.01). A consistently lower survival rate was expected when the lung was evaluated distant to the ultrasound probe. Conclusions Lung size estimation in L‐CDH fetuses may be affected by fetal position, which may affect postnatal prognosis, prediction of survival and eligibility for fetal therapy.