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

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.

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.

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.

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.