FETAL INFLOW HYDROSTATIC PRESSURE MEASUREMENTS IN THE EX-VIVO PERFUSED PLACENTA CORRELATE WITH UMBILICAL ARTERY DOPPLER RI AND PI VALUES

Elevated resistance and pulsatility indices (RI & PI) in the umbilical arterial circulation measured clinically by Doppler waveform velocimetry are indicative of poor pregnancy outcome; additionally elevated indices are assumed to represent increased resistance to flow in the placental vasculature. Vascular resistance in the fetoplacental circulation can be investigated using ex-vivo dual perfusion of the human placental cotyledon. The aim of this study was to test the hypothesis that fetal-side inflow hydrostatic pressure (FIHP) measured ex-vivo using dual placental perfusion reflects umbilical artery Doppler measurements of vascular resistance performed in vivo. Umbilical artery Doppler RI and PI were performed on women (n=9) at term, 1-4h prior to delivery by Caesarean section. Following delivery, dual perfusion of placental cotyledons was performed at flow rates of 6ml/min and 12ml/min and FIHP measured as an indication of vascular resistance. A strong positive correlation was observed when comparing PI measurements performed in vivo to the subsequent ex-vivo FIHP measurements in the perfused placenta at flow rates of 6ml/min (Spearman r=0.853, P=0.0061) and 12ml/min (Spearman r=0.8228, P=0.0083). Correlations between in vivo RI measurements and FIHP values demonstrated an even stronger positive correlation (Spearman r=0.9664, P=0.0002 and 0.9494, P=0.0004) at flow rates of 6ml/min and 12ml/min respectively. These data indicate that umbilical artery Doppler waveforms are reflective of the degree of downstream vascular resistance to fetal blood flow, which is determined at placental level. In conclusion, we provide further supportive evidence that the ex-vivo dual placental perfusion serves as a relevant model for investigating vascular resistance in the fetoplacental circulation.