Background: Children with complex congenital heart defects (CHD) have significantly decreased brain size before birth and are at increased risk of neurodevelopmental impairment compared to children born without CHD. Knowledge about intrauterine growth of other organs in fetuses with CHD is limited. 

Objective: To determine if lung growth is affected in fetuses with CHD using fetal Magnetic Resonance (MR)-imaging.

Methods: Eight fetuses with transposition of the great arteries (TGA) without other concomitant disease or chromosomal abnormalities and 42 fetuses without CHD were scanned once or twice at gestational age 30 through 39 weeks. The MR-scans were conducted on a 1.5T system, using a TrueFISP-sequence. Slices acquired covered the entire fetus, slice thickness was 10mm, pixel size 1.5x1.5mm, and scan duration was 30 sec. A blinded observer measured lung volumes and compared those with and without TGA using difference in means, linear regression, Mann-Whitney U-testing, and correcting for Estimated Fetal Weight. Intra- and inter-observer reliability of the measured lung volumes were assessed through Intraclass Correlation Coefficient (ICC) and Bland Altman Plots. An in vitro pilot study, using the same MRI parameters as for the fetal MR images, was conducted to determine the validity of MR-volumetrics. 

Results: Mean lung volume for fetuses without TGA was 76.9cm3 (95%CI: [71.1; 82.7]cm3) and for TGA-fetuses 103.3cm3 (95%CI: [86.2; 119.8]cm3). The lung size in fetuses with TGA, was larger than the fetuses without TGA with a mean difference of 0.01cm3/g 95%CI: [0.002; 0.012.86] cm3/g, p=0.004 when corrected for Estimated Fetal Weight. ICC of the lung volume measurements was 0.96. Deviations from true volume between -3.3% and -2.5% were found in the in-vitro pilot study

Conclusion: Surprisingly, TGA-fetuses had larger lung volumes than those without a congenital heart defect. This warrants further investigation. Overall, there was a high reliability of the lung volume measurements. However, the small number of cases in this project should be considered.