The effect of maternal pushing on fetal cerebral oxygenation and blood volume during the second stage of labour

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 oxyhaemoglobin, 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) mumol.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.