Inferior vena cava flow velocity waveforms relative to fetal behavioural states and sample site in normal term...

Reproducibility and behavioural state dependency of flow velocity waveforms from the proximal and distal part of the fetal inferior vena cava were studied in a total of 27 normal pregnancies at 36-39 weeks of gestation. Within patient coefficients of variation in fetal inferior vena cava waveform recording were markedly higher for the proximal part compared with the distal part. This is also reflected by lower reliability values as a measure of the relative proportion of within patient and between patient variance components. No statistically significant changes in flow velocity values could be detected at proximal and distal level of the fetal inferior vena cava relative to fetal behavioural states. A marked difference in flow velocity values was, however, observed between the two measuring sites with the highest velocities at proximal level. Since a considerable variation in fetal inferior vena cava flow recording was established, a possible behavioural state related modulation may have been obscured by these waveform variabilities.