Institute of Medical Science, Temerty Faculty of Medicine, University of Toronto, Toronto, ON, M5S 1A8, Canada.
Division of Cardiology, Labatt Family Heart Centre, The Hospital for Sick Children, Toronto, ON, M5G 1X8, Canada.
J Physiol. 2021 May;599(10):2573-2602. doi: 10.1113/JP281002. Epub 2021 Mar 29.
Human placental function is evaluated using non-invasive Doppler ultrasound of umbilical and uterine artery pulsatility indices as measures of resistance in placental vascular beds, while measurement of placental oxygen consumption ( ) is only possible during Caesarean delivery. This study shows the feasibility of using magnetic resonance imaging (MRI) in utero to measure blood flow and oxygen content in uterine and umbilical vessels to calculate oxygen delivery to and by the gravid uterus, uteroplacenta and fetus. Normal late gestational human uteroplacental by MRI was ∼4 ml min kg fetal weight, which was similar to our MRI measurements in sheep and to those previously measured using invasive techniques. Our MRI approach can quantify uteroplacental , which involves the quantification of maternal- and fetal-placental blood flows, fetal oxygen delivery and , and the oxygen gradient between uterine- and umbilical-venous blood, providing a comprehensive assessment of placental function with clinical potential.
It has not been feasible to perform routine clinical measurement of human placental oxygen consumption ( ) and in vitro studies do not reflect true metabolism in utero. Here we propose an MRI method to non-invasively quantify in utero placental and fetal oxygen delivery ( ) and in healthy humans and sheep. Women (n = 20) and Merino sheep (n = 10; 23 sets of measurements) with singleton pregnancies underwent an MRI in late gestation (36 ± 2 weeks and 128 ± 9 days, respectively; mean ± SD). Blood flow (phase-contrast) and oxygen content (T1 and T2 relaxometry) were measured in the major uterine- and umbilical-placental vessels, allowing calculation of uteroplacental and fetal and . Maternal (ml min kg fetus) to the gravid uterus was similar in humans and sheep (human = 54 ± 15, sheep = 53 ± 21, P = 0.854), while fetal (human = 25 ± 4, sheep = 22 ± 5, P = 0.049) was slightly lower in sheep. Uteroplacental and fetal (ml min kg fetus; uteroplacental: human = 4.1 ± 1.5, sheep = 3.5 ± 1.9, P = 0.281; fetus: human = 6.8 ± 1.3, sheep = 7.2 ± 1.7, P = 0.426) were similar between species. Late gestational uteroplacental:fetal ratio did not change with age (human, P = 0.256; sheep, P = 0.121). Human umbilical blood flow (ml min kg fetus) decreased with advancing age (P = 0.008), while fetal was preserved through an increase in oxygen extraction (P = 0.046). By contrast, sheep fetal was preserved through stable umbilical flow (ml min kg ; P = 0.443) and oxygen extraction (P = 0.582). MRI derived measurements of uteroplacental and fetal between humans and sheep were similar and in keeping with prior data obtained using invasive techniques. Taken together, these data confirm the reliability of our approach, which offers a novel clinical 'placental function test'.
用脐动脉和子宫动脉搏动指数等非侵入性多普勒超声评估胎盘功能，作为胎盘血管床阻力的指标，而胎盘耗氧量（ ）的测量仅在剖宫产时才有可能。本研究表明，在子宫内使用磁共振成像（MRI）测量子宫和脐带血管的血流和氧含量，以计算向妊娠子宫、胎盘和胎儿输送的氧和 ，这是可行的。晚期妊娠正常人类的子宫胎盘 （ml/min/kg 胎儿体重）为 4ml/min/kg 胎儿体重，与我们在绵羊中的 MRI 测量值以及以前使用侵入性技术测量的值相似。我们的 MRI 方法可以定量胎盘 ，包括量化母体和胎儿胎盘血流、胎儿氧输送和 、子宫静脉和脐静脉血之间的氧梯度，为胎盘功能提供全面的评估，具有临床潜力。
目前还无法对人类胎盘耗氧量（ ）进行常规临床测量，体外研究也不能反映子宫内的真实代谢情况。在这里，我们提出了一种 MRI 方法，用于非侵入性地定量测量健康人类和绵羊的子宫内和胎儿的氧输送（ ）和 。20 名孕妇（n=20）和美利奴羊（n=10；23 对测量）在晚期妊娠（分别为 36±2 周和 128±9 天；均值±SD）进行了 MRI 检查。在主要的子宫-胎盘血管中测量血流（相位对比）和氧含量（T1 和 T2 弛豫时间测量），从而计算子宫胎盘和胎儿的 和 。向妊娠子宫的母体 （ml/min/kg 胎儿）在人类和绵羊中相似（人类=54±15，绵羊=53±21，P=0.854），而胎儿 （人类=25±4，绵羊=22±5，P=0.049）在绵羊中略低。子宫胎盘和胎儿 （ml/min/kg 胎儿；子宫胎盘：人类=4.1±1.5，绵羊=3.5±1.9，P=0.281；胎儿：人类=6.8±1.3，绵羊=7.2±1.7，P=0.426）在两种物种之间相似。晚期妊娠子宫胎盘：胎儿 比值不随年龄变化（人类，P=0.256；绵羊，P=0.121）。人类脐动脉血流（ml/min/kg 胎儿）随年龄增长而减少（P=0.008），而胎儿 则通过增加氧摄取来维持（P=0.046）。相比之下，绵羊胎儿 通过稳定的脐血流（ml/min/kg；P=0.443）和氧摄取（P=0.582）来维持。人类和绵羊之间通过 MRI 获得的子宫胎盘和胎儿 测量值相似，与以前使用侵入性技术获得的数据一致。综上所述，这些数据证实了我们的方法的可靠性，为临床“胎盘功能测试”提供了一种新方法。
