Human fetal foramen ovale flow velocity waveforms relative to behavioral states in normal term pregnancy.

In 16 normal pregnancies the relationship between foramen ovale flow velocity waveforms and fetal behavioral states at 37 to 38 weeks' gestation was studies with Doppler techniques. Foramen ovale flow velocity waveforms are characterized by a typical systolic/diastolic component. Average flow velocity was statistically significantly increased in behavioral state 2F (active sleep) as compared with state 1F (quiet sleep), which was mainly determined by an increase in flow velocity during the end-systolic and passive atrial filling phase. The increase in the average flow velocity at the foramen ovale level during active sleep suggests a redistribution of blood flow at the cardiac level, resulting in an increased right-to-left shunt.