Obstetric Analgesia and Fetal Aortic Blood Flow During Labour

Fetal aortic blood flow was studied in 50 women during labour, using a method combining real-time ultrasonography and a pulsed Doppler technique. Eleven women had no analgesia, 24 women received 75-100 mg pethidine intramuscularly, 12 epidural analgesia with 0.25% bupivacaine and three paracervical block with 0.125% bupivacaine. Fetal aortic blood flow increased during labour from 200 to 245 ml/min/kg in the group without analgesia (P less than 0.05) and from 211 to 236 ml/min/kg in the group with epidural analgesia (P less than 0.05) but decreased insignificantly from 216 to 204 ml/min/kg after pethidine. After paracervical block the aortic blood flow fell in two out of three fetuses. Not only is epidural analgesia the most effective means of pain relief during labour, it is also the type of obstetric analgesia that interferes least with the physiological response to labour in terms of its effect on the fetal blood flow.