Dynamic Fetal and Placental Circulatory Changes during Uterine Contractions

Sammanfattning: The best mode of delivery for fetuses with intrauterine growth restriction (IUGR) and umbilical artery (UA) blood flow changes is not well elucidated. Uterine artery, fetal UA, middle cerebral artery (MCA), and venous blood flow changes during uterine contractions during an oxytocin challenge test (OCT) have not been observed systemically. AIMS: To evaluate outcome in IUGR with UA blood flow changes planned for vaginal delivery after a negative OCT, and to investigate uterine artery, fetal UA, MCA, and venous blood flow during OCT with Doppler ultrasound. RESULTS: 1. A positive OCT occurred twice as often in IUGR with abnormal UA blood flow as in IUGR with normal flow. In OCT negative cases allowed a trial of labor, the vaginal delivery rate was not different between the two flow groups. 2. Doppler velocimetry of blood flow velocity waveforms (FVWs) during uterine quiescence, contractions and relaxations in the uterine arteries identified 11 different waveform shapes when recordings were systemically classified with regard to the mean flow velocity over the pulse cycle. 3. No different uterine artery blood flow changes during the OCT were found in cases with or without operative delivery for fetal distress (ODFD) or birth asphyxia. 4. The UA vascular flow resistance was significantly higher in OCT positive cases compared with negative cases during uterine contractions and relaxations, but not during basal measurements; No different UA blood flow changes during the OCT were found in cases with or without ODFD or birth asphyxia. 5. The vascular flow resistance in fetal MCA decreased during uterine contractions and relaxations compared with basal measurements both in OCT positive and negative cases, but OCT positive cases showed a more pronounced decrease. 6. Increased blood flow velocities and decreased impedance to flow occurred in fetal cerebral veins parallel to a decrease of vascular flow resistance in the fetal MCA during uterine contractions. CONCLUSIONS: OCT was just as good in the abnormal flow group as in the normal flow group to select suitable candidates for a trial of vaginal delivery. The proposed qualitative classification system may accomplish to cover a complete spectrum of different uterine artery FVWs, but uterine artery blood FVWs during the OCT seems have a limited clinical value in predicting pregnancy outcome. A vascular pathophysiological mechanism operating in OCT positive cases was disclosed only during the OCT, but an ‘OCT Doppler velocimetry?of UA blood flow seems to have a limited predictive value on neonatal outcome. A redistribution of the fetal circulation with a ‘brain-sparing?flow is a physiological phenomenon occurring during acute hypoxemia provoked by uterine contractions.