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 Doppler 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 intrapartum 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.