Exploration of 3D fetal cardiac MRI in the late second trimester

Fetal cardiovascular magnetic resonance imaging (CMR) is restricted to late gestation due to fetal movement and vessel size while initial clinical assessment of the fetal heart is conducted mid-trimester. This study aimed to assess feasibility and diagnostic potential of automated motion-correction tools for 3D fetal CMR of late second trimester fetuses.

Black-blood fetal CMR datasets of controls and fetuses with congenital heart disease (CHD) (20 - 27⁺⁶ weeks' gestation) were collected and reconstructed to 3D volumes. Image quality, nineteen cardiovascular structures and sequential segmental analysis were assessed. Correlation with gestational age, fetal body volume and maternal BMI was investigated.

142 controls were included (median gestation 24.4 weeks, IQR 23.4 - 25.7). Image quality was adequate or high in 119/142 (84%), poor in 22/142 (16%), and inadequate in one. In total, 48/2679 (2%) cardiac structures were not visualised. Completion of vascular segmental assessment was high across all four areas (84-98%). Maternal girth and BMI showed a weak negative correlation with image quality. Number of input stacks had a weak positive correlation with vessel visualisation. Six CHD cases were assessed; pathognomonic vascular features were identified in 5/6 by at least one blinded observer.

This study demonstrates feasibility of 3D fetal cardiac MRI for detailed assessment of the fetal cardiovascular system before 28 weeks' gestation. Overall performance, image quality and visualisation of vascular structures was high, and visualisation of vascular anomalies was demonstrated. This creates new potential for improving antenatal diagnosis of major vascular anomalies in second trimester fetuses.