Fetal middle cerebral artery blood flow during normal active labour and in labour with variable decelerations

ABSTRACT Objective To assess the distribution of fetal blood flow impedance of the umbilical and middle cerebral artery in active uncomplicated labour and in labour complicated by variable decelerations. Interventions Blood flow impedance of the umbilical and fetal middle cerebral arteries was assessed by means of pulsed Doppier ultrasonography and measured by the resistance index (RI) and the systolic/diastolic ratio. Subjects 35 women at 38–40 weeks gestation admitted to, or monitored in the intra‐partum unit. One group of 25 women had a normal active labour, the second group of 10 women were in active labour with moderate variable decelerations. A control group of 25 women—healthy pregnant women at term but not in active labour. All three groups were comparable for maternal age and parity. Setting Hospital department of Obstetrics and gynaecology, Israel. Design A prospective descriptive study. Results There was a 40% reduction in middle cerebral artery blood flow impedance in the two groups of women in active labour compared with the control group. Umbilical blood flow did not differ significantly between the three groups. Fetal middle cerebral blood flow impedance in labour was not significantly different in uncomplicated labours and those complicated by fetal heart rate decelerations. Conclusions During active labour, mechanisms that may be unrelated to low fetal blood oxygen content reduce fetal brain blood vessel impedance.