Objective To measure the effect of maternal pushing during the second stage of labour on fetal cerebral oxygenation and blood volume.
Design A prospective study comparing changes in the fetal cerebral concentrations of oxy-haemoglobin, deoxyhaemoglobin and cerebral blood volume, before and during maternal pushing in the second stage of labour.
Setting Teaching hospital obstetric unit.
Subjects Ten term fetuses during labour.
Results Following the onset of maternal pushing, mean cerebral deoxyhaemoglobin concentration increased by a mean of 0.79 (SD 0.59) μmol.100 g-1, (P < 0.01) without any consistent change in the oxyhaemoglobin concentration. These changes were associated with a significant decrease in the calculated mean cerebral oxygen saturation from a mean of 46.8% (SD 8.6) to 38.1% (SD 5.2) (P < 0.01). Pushing was also associated with a significant increase in the mean cerebral blood volume, which rose by a mean of 0.33 ml. 100 g-1 (SD 0.37) (P < 0.05).
Conclusion Maternal pushing during the second stage of labour leads to a significant decrease in fetal cerebral oxygenation, together with an increase in cerebral blood volume.