Comparison of Cardiac Function between Uncomplicated Monozygotic Twins and Singleton Fetuses in the Second Trimester by Fetal <scp>HQ</scp> : A Pilot Study

OBJECTIVES: To compare cardiac morphology and function between uncomplicated monochorionic diamniotic (MCDA) twin and singleton fetuses during the second trimester using the fetal heart quantification (Fetal HQ) technique. METHODS: This prospective study included 47 MCDA twin pregnancies (165 ultrasound examinations) and 165 gestational age (GA)-matched singleton pregnancies between 16 and 27 weeks. Cardiac parameters were assessed using Fetal HQ and compared between groups, along with correlations with GA. RESULTS: MCDA fetuses showed higher global sphericity index (GSI) and reduced systolic function, with lower left ventricular ejection fraction (LV-EF), right ventricular global longitudinal strain (RV-GLS), left ventricular fractional area change (LV-FAC), and right ventricular fractional area change (RV-FAC), as well as fractional shortening (FS) across all 24 segments of both the left and right ventricles (all adjusted p < .05). LV sphericity index (SI) was increased in segments 1-3, 21-24, and RV SI in segments 20-24 (adjusted p < .05) in MCDA fetuses. No significant differences were observed for other parameters. In MCDA fetuses, overall parameters showed no correlation with GA (all p > .05), while singletons showed significant correlations (r = -0.35 ∼ 0.23, p < .05). Segmental end-diastolic diameter (ED) of both ventricles was positively correlated with GA in both groups (all r > 0.75, all p < .01). FS was negatively correlated with GA in singleton LV segments 1-7 and all RV segments, as well as in MCDA RV segments 6-17 (r = -0.31 ∼ -0.16, p < .05). For SI, both the MCDA and singleton groups demonstrated negative correlations between LV apical segments and GA (r = -0.18 ∼ -0.16, p < .05). CONCLUSIONS: During the mid-trimester, uncomplicated MCDA twins exhibit distinct cardiac geometry and subtle differences in systolic performance compared to singletons, with possible differences in the developmental trajectory of cardiac parameters. These data suggest that twin-specific reference ranges may ultimately be required to distinguish normal development from early dysfunction.