Assessment of lung area in fetuses with congenital diaphragmatic hernia.

OBJECTIVE To compare the intra- and interobserver agreement of three different methods of measuring lung area in fetuses with congenital diaphragmatic hernia (CDH). METHODS In 71 fetuses with isolated CDH at 21-33 weeks' gestation, the area of the contralateral lung was assessed by firstly, manual tracing of lung borders, secondly, multiplication of the longest diameter of the lung by its widest perpendicular diameter, and thirdly, multiplication of the anteroposterior (AP) diameter of the lung at the mid-clavicular line by the perpendicular diameter at the midpoint of the AP diameter (AP method). In 30 fetuses the measurements were made by two observers and Bland-Altman analysis was used to compare the measurement agreement and bias for each observer and between the two observers. RESULTS The area obtained by the AP method was similar to that obtained by the manual tracing method, but the area by the longest diameter approach was bigger by 34.4% (95% CI, - 2.4% to 71.1%). The 95% confidence intervals of the difference in paired measurements of lung areas by the same observer and by two different observers were narrower in the manual tracing method than in the multiplying diameters methods. CONCLUSIONS In CDH the most reproducible measurement of fetal lung area is provided by manual tracing of the limits of the lungs, rather than by multiplication of lung diameters.