OBJECTIVE: We hypothesized that a decrease in fetal oxygenation without acidemia in a near-term fetal sheep leads to cardiovascular hemodynamic changes that are detectable by Doppler ultrasonography. STUDY DESIGN: Twelve ewes and fetuses were instrumented at 112 to 127 days of gestation. After a 5-day recovery period, experiments were performed with general anesthesia. Uterine and placental volume blood flows and fetal arterial and venous blood pressures were measured. Fetal cardiovascular hemodynamics was assessed by Doppler ultrasonography. All the measurements were performed at baseline, during fetal hypo-oxygenation, and at recovery phase. RESULTS: A drop in fetal Po2 was related to increased (P