The Doppler flow velocity waveform in the fetal internal carotid artery with respect to fetal behavioural states. A longitudinal study.

Doppler flow velocity waveforms in the fetal internal carotid artery were recorded in 21 normal pregnancies during fetal behavioural state IF (quiet sleep) and 2F (active sleep) according to Nijhuis and co-workers, from the 36th week of gestation onwards. The present study confirms the earlier finding of a significant reduction of the pulsatility index (PI) in state 2F as compared to state IF at 37–38 weeks of gestation and demonstrates that this difference in PI exists throughout the entire period, in which fetal behavioural states have been described. Furthermore, it is demonstrated that there is a significant reduction in PI of this vessel during the last 4 weeks of gestation, suggesting a haemodynamic redistribution, favouring blood supply to the brain during the latter weeks of gestation.