妊娠晚期仰卧位减少了由于下腔静脉(IVC)压迫引起的母体心输出量,尽管侧支静脉回流增加。然而,对母体位置对妊娠子宫的氧气(O2)输送和消耗的影响知之甚少,胎儿,胎盘和下肢。我们使用磁共振成像(MRI)在36±2周时研究了20名健康孕妇的母体定位对这些参数的影响;产后6个月进行了MRI随访(n=16/20)。MRI技术包括用于血流和血氧饱和度成像的相位对比和T1/T2弛豫测量,分别。在以下血管(适当时,双侧)中测量O2转运:母体腹降主动脉(DAoabdo),IVC,卵巢,椎旁静脉(PSV),子宫动脉(UtA)和外髂动脉,和脐带。通过将DAthoracic和上腔静脉流量求和来测量母体心输出量。在DAoabdo中,仰卧母亲(n=6)的心输出量和O2分娩较低,UtA和髂外动脉,在MRI期间,PSV流量高于左侧(n=8)或右侧(n=6)的水平。然而,妊娠子宫的O2消耗,胎儿,胎盘和下肢不受母体定位的影响.仰卧位母亲的IVC/PSV流量比率降低,而卵巢静脉流量和O2饱和度未改变,提示盆腔静脉回流的主要途径不受产妇位置的影响。左右两侧母体位置之间的胎盘-胎儿O2运输和消耗相似。与非怀孕的发现相比,DAoabdo和UtAO2输送和骨盆O2消耗增加,而下肢消耗保持不变,尽管妊娠晚期髂外动脉O2分娩减少。关键点:虽然在妊娠晚期仰卧睡眠与产前死胎的风险增加有关,潜在的生物学机制尚未完全了解。由于妊娠子宫重量的下腔静脉压迫,仰卧母亲的母亲心输出量和子宫胎盘流量减少。这项MRI研究提供了全面的循环评估,证明母体心输出量和O2输送减少(子宫胎盘,与横向定位相比,仰卧);然而,O2消耗(妊娠子宫,胎儿,胎盘,下肢)被保存。与其他哺乳动物不同,卵巢静脉从孕妇子宫进行大量静脉回流,不受孕妇位置的影响。仰卧位母亲的腰椎旁静脉流量增加。这些观察结果在妊娠大盆腔手术(即胎盘)期间可能有重要的考虑因素。未来的研究应该解决产妇定位的重要性,作为一种潜在的工具,在子宫胎盘O2分娩受损的妊娠中改善围产期结局。
Late gestational supine positioning reduces maternal cardiac output due to inferior vena caval (IVC) compression, despite increased collateral venous return. However, little is known about the impact of maternal position on oxygen (O2 ) delivery and consumption of the gravid uterus, fetus, placenta and lower limbs. We studied the effects of maternal positioning on these parameters in 20 healthy pregnant subjects at 36 ± 2 weeks using magnetic resonance imaging (MRI); a follow-up MRI was performed 6-months postpartum (n = 16/20). MRI techniques included phase-contrast and T1/T2 relaxometry for blood flow and oximetry imaging, respectively. O2 transport was measured in the following vessels (bilateral where appropriate): maternal abdominal descending aorta (DAoabdo ), IVC, ovarian, paraspinal veins (PSV), uterine artery (UtA) and external iliacs, and umbilical. Maternal cardiac output was measured by summing DAothoracic and superior vena cava flows. Supine mothers (n = 6) had lower cardiac output and O2 delivery in the DAoabdo , UtA and external iliac arteries, and higher PSV flow than those in either the left (n = 8) or right (n = 6) lateral positions during MRI. However, O2 consumption in the gravid uterus, fetus, placenta and lower limbs was unaffected by maternal positioning. The ratio of IVC/PSV flow decreased in supine mothers while ovarian venous flow and O2 saturation were unaltered, suggesting a major route of pelvic venous return unaffected by maternal position. Placental-fetal O2 transport and consumption were similar between left and right lateral maternal positions. In comparison to non-pregnant findings, DAoabdo and UtA O2 delivery and pelvic O2 consumption increased, while lower-limb consumption remained constant , despite reduced external iliac artery O2 delivery in late gestation. KEY POINTS: Though sleeping supine during the third trimester is associated with an increased risk of antepartum stillbirth, the underlying biological mechanisms are not fully understood. Maternal cardiac output and uteroplacental flow are reduced in supine mothers due to inferior vena caval compression from the weight of the gravid uterus. This MRI study provides a comprehensive circulatory assessment, demonstrating reduced maternal cardiac output and O2 delivery (uteroplacental, lower body) in supine compared to lateral positioning; however, O2 consumption (gravid uterus, fetus, placenta, lower limbs) was preserved. Unlike other mammalian species, the ovarian veins conduct substantial venous return from the human pregnant uterus that is unaffected by maternal positioning. Lumbar paraspinal venous flow increased in supine mothers. These observations may have important considerations during major pelvic surgery in pregnancy (i.e. placenta percreta). Future studies should address the importance of maternal positioning as a potential tool to deliver improved perinatal outcomes in pregnancies with compromised uteroplacental O2 delivery.