The effect of fetal heart rate on umbilical artery flow velocity waveforms.

Umbilical artery flow velocity waveforms were obtained using continuous wave Doppler ultrasound in 85 normal pregnancies (25 antepartum, 60 intrapartum) to examine the relation between fetal heart rate, end systolic/end diastolic ratio (A/B ratio) and resistance index (RI). Our results demonstrated a significant negative correlation between fetal heart rate, A/B ratio and RI (in the antepartum group r = -0.49, and in the labouring group r = -0.65). It is therefore important when performing mathematical analysis of umbilical artery flow velocity profiles to make a statistical allowance for fetal heart rate.