BACKGROUND: Doppler ultrasound has recently been used to assess change in blood velocity in the uterine and umbilical arteries. Alterations in the ratio of systolic to diastolic velocity (= S/D ratio) are believed to reflect changes in placental vascular resistance. We have used this technique to assess potential beneficial or detrimental effects of epidural anesthesia on blood flow to the placenta. METHODS: Continuous wave Doppler ultrasound was used to measure the S/D ratio in the uterine and umbilical arteries of 40 patients undergoing epidural anesthesia prior to elective cesarean section. Left uterine displacement was employed throughout. Doppler ultrasound obtained at the level of umbilical artery and uterine artery. Prior to induction of anesthesia each patient received 800~1,000 ml of lactated Ringer's solution within 20~30 minutes. For epidural anesthesia 2% lidocaine 10 ml and 0.5% bupivacaine 10 ml were used. An upper level of sensory anesthesia to at least T10 was confirmed before umbilical and uterine artery waveform measurement. RESULTS: Epidural anesthesia was followed by a reduction in umbilical artery systolic : diastolic ratio from 2.48+/-0.5 to 2.24+/-0.40 (p<0.05) and in uterine artery systolic : diastolic ratio from 2.29+/-0.41 to 1.96+/- 0.25 (p<0.05). CONCLUSIONS: Epidural anesthesia for cesarean section resulted in a significant decrease in the maternal uterine artery S/D ratio and fetal umbilical artery S/D ratio. This study suggests beneficial fetal effect from the improved maternal uterine perfusion after epidural anesthesia.