Low oxygen levels in the fetus, commonly as a result of diminished placental perfusion, uteroplacental insufficiency, or umbilical cord compression. The condition often is accompanied by acidosis and is life-threatening unless prompt interventions are undertaken to restore well-oxygenated blood to the fetus. Signs of early fetal hypoxia include tachycardia and increased fetal heart rate variability; profound fetal hypoxia is characterized by bradycardia and a sinusoidal fetal heart rate pattern.