Reference Values for Fetal Cardiac Dimensions, Volumes, Ventricular Function and Left Ventricular Longitudinal Strain Using Doppler Ultrasound Gated Cardiac Magnetic Resonance Imaging in Healthy Third Trimester Fetuses

Background: Recent advances in hardware and software permit the use of cardiac MRI of late gestation fetuses, however there is a paucity of MRI-based reference values.Purpose: To provide initial data on fetal cardiac MRI-derived cardiac dimensions, volumes, ventricular function, and left ventricular longitudinal strain in healthy developing fetuses >30 weeks gestational age.Study type: Prospective.Population: Twenty-five third trimester (34 +/- 1 weeks, range of 32-37 weeks gestation) women with healthy developing fetuses.Field strength/sequence: Studies were performed at 1.5 T and 3 T. Cardiac synchronization was achieved with a Doppler ultrasound device. The protocol included T2 single shot turbo spin echo stacks for fetal weight and ultrasound probe positioning, and multiplanar multi-slice cine balanced steady state free precession gradient echo sequences.Assessment: Primary analyses were performed by a single observer. Weight indexed right ventricular (RV) and left ventricular (LV) volumes and function were calculated from short axis (SAX) stacks. Cardiac dimensions were calculated from the four-chamber and SAX stacks. Single plane LV longitudinal strain was calculated from the four-chamber stack. Interobserver variability was assessed in 10 participants. Cardiac MRI values were compared against available published normative fetal echocardiogram data using z-scores.Statistical tests: Mean and SDs were calculated for baseline maternal/fetal demographics, cardiac dimensions, volumes, ventricular function, and left ventricular longitudinal strain. Bland-Altman and intraclass correlation coefficient analysis was performed to test interobserver variability.Results: The mean gestational age was 34 +/- 1.4 weeks. The mean RV and LV end diastolic volumes were 3.1 +/- 0.6 mL/kg and 2.4 +/- 0.5 mL/kg respectively. The mean RV cardiac output was 198 +/- 49 mL/min/kg while the mean LV cardiac output was 173 +/- 43 mL/min/kg.Data conclusion: This paper reports initial reference values obtained by cardiac MRI in healthy developing third trimester fetuses. MRI generally resulted in slightly larger indexed values (by z-score) compared to reports in literature using fetal echocardiography.

Automated summary

This study aims to provide initial data on cardiac dimensions, volumes, ventricular function, and left ventricular longitudinal strain in healthy developing fetuses using cardiac MRI. The results showed that the indexed values obtained by MRI were slightly larger compared to the literature reports using fetal echocardiography.