Plasma catecholamines and modes of delivery: the relation between catecholamine levels and in-vitro platelet aggregation and adrenoreceptor radioligand binding characteristics.

Catecholamines were measured in maternal venous, and mixed umbilical cord blood. Maternal catecholamines were significantly (P less than 0.01) reduced by epidural analgesia with a 36% reduction in noradrenaline and a 33% reduction in adrenaline. Fetal catecholamines were elevated at birth with a 3-8 fold increase in noradrenaline but not adrenaline during spontaneous vaginal delivery. The lowest fetal catecholamines were obtained in the group delivered under epidural analgesia; lower plasma catecholamines were not associated with adverse respiratory effects. Fetal platelets showed impaired alpha 2-adrenoceptor function with absent aggregatory responses to adrenaline in vitro. The defect in platelet function was unlikely to be related to changes in the number of fetal platelet alpha-receptors or to changes in receptor affinity for adrenaline, as fetal platelets failed to aggregate to adrenaline from deliveries with high and low cord blood catecholamines.