Feasibility of fetal cardiac output measurement by phase contrast magnetic resonance imaging using Doppler ultrasound gating increases with gestational age.

Background: Fetal magnetic resonance imaging (MRI) is a valuable tool for assessing fetal blood flow; however, its use has primarily been focused on near-term pregnancies. This study aimed to evaluate the feasibility of Doppler ultrasound-gated 2D phase-contrast cardiac MRI of the human fetus in the early, mid, and late third trimester.

Methods: A total of 100 fetal MRI scans were performed at gestational age (GA) 28, 32 and 38 weeks in 38 fetuses with (n=13) and without (n=25) congenital heart defects. Combined ventricular output was measured by Doppler ultrasound gated 2D phase contrast MRI in the ascending aorta and main pulmonary artery. Success rate of acquisition, repeatability of phase contrast-measurements and intra-/interobserver agreement were assessed at each GA.

Results: Combined ventricular output was obtained in 76/100 (76%) scans. The success rate of acquisition improved with increasing GA from 15/34 (44%) at GA 28 weeks to 31/35 (89%) at GA 32 weeks (p <0.001 compared to 28 weeks) and 30/31 (97%) at GA 38 weeks (p <0.001 compared to 28 weeks). Repeatability of phase contrast measurements demonstrated a moderate to strong correlation (r = 0.63 - 0.82, p = 0.002), with no significant bias but wide limits of agreement. The mean difference ±95% limits of agreement were 7.3±245mL/min, -13.0±260mL/min, and -3.9±326mL/min at 28, 32, and 38 weeks, respectively.

Conclusion: Feasibility of fetal cardiac MRI improves with increasing GA. While Doppler-gated 2D phase contrast MRI can effectively assess fetal combined ventricular output and allows for in-group comparisons, the precision may still be insufficient for clinical application.