| Sumario: | To compare fetal left ventricular Tei index (TI) values and hemodynamic correlations between high-altitude and low-altitude pregnancies, establishing an altitude-specific framework for fetal cardiac assessment. This prospective dual-group study enrolled 234 high-altitude and 252 low-altitude singleton pregnancies in Yunnan, China. Standardized Doppler ultrasound was performed at 20–25, 30–34, and 37–40 weeks. Fetal TI and hemodynamic parameters (umbilical artery [UA], ductus venosus [DV], middle cerebral artery [MCA], uterine artery [UtA]) were measured using a Samsung WS80A ultrasound system with strict angle control (<20° for vessels, <15° for TI). TI elevation: High-altitude TI was consistently higher (all p<0.001): 20–25 w: 0.471 ± 0.027 vs. 0.405 ± 0.131 (Δ16.3 %); 30–34 w: 0.492 ± 0.050 vs. 0.384 ± 0.121 (Δ28.1 %); 37–40 w: 0.484 ± 0.052 vs. 0.365 ± 0.148 (Δ32.6 %). Gestational divergence: TI decreased with gestation in high-altitude group (F=4.037, p=0.019) but remained stable in low-altitude group (F=1.421, p=0.244). TI was negatively correlated with dominant TI-MCA-PSV (r=−0.383) and TI-DV-PAV (r=−0.314) at high altitude, while showing a positive correlation with Strongest TI-UA-S/D (r=0.257) at low altitude. Chronic hypoxia induces a distinct fetal cardiovascular phenotype characterized by Tei index elevation (>0.48 post-30w), venous compromise (DV-PAV), and cerebral compensation (MCA-PSV). The tri-parametric model (TI + DV-PAV + MCA-PSV) addresses critical gaps in altitude-agnostic guidelines, offering tailored surveillance for 140 million high-altitude pregnancies globally.
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