Institute of Medical Science, University of Toronto, Toronto, ON, Canada; Division of Cardiology, Mount Sinai Hospital, University of Toronto, ON, Canada.
Department of Obstetrics and Gynecology, Mount Sinai Hospital, University of Toronto, Toronto, ON, Canada.
Am J Obstet Gynecol. 2016 Mar;214(3):367.e1-367.e17. doi: 10.1016/j.ajog.2015.10.004. Epub 2015 Oct 22.
Late-onset intrauterine growth restriction (IUGR) results from a failure of the placenta to supply adequate nutrients and oxygen to the rapidly growing late-gestation fetus. Limitations in current monitoring methods present the need for additional techniques for more accurate diagnosis of IUGR in utero. New magnetic resonance imaging (MRI) technology now provides a noninvasive technique for fetal hemodynamic assessment, which could provide additional information over conventional Doppler methods.
The objective of the study was to use new MRI techniques to measure hemodynamic parameters and brain growth in late-onset IUGR fetuses.
This was a prospective observational case control study to compare the flow and T2 of blood in the major fetal vessels and brain imaging findings using MRI. Indexed fetal oxygen delivery and consumption were calculated. Middle cerebral artery and umbilical artery pulsatility indexes and cerebroplacental ratio were acquired using ultrasound. A score of ≥ 2 of the 4 following parameters defined IUGR: (1) birthweight the third centile or less or 20% or greater drop in the centile in estimated fetal weight; (2) lowest cerebroplacental ratio after 30 weeks less than the fifth centile; (3) ponderal index < 2.2; and (4) placental histology meets predefined criteria for placental underperfusion. Measurements were compared between the 2 groups (Student t test) and correlations between parameters were analyzed (Pearson's correlation). MRI measurements were compared with Doppler parameters for identifying IUGR defined by postnatal criteria (birthweight, placental histology, ponderal index) using receiver-operating characteristic curves.
We studied 14 IUGR and 26 non-IUGR fetuses at 35 weeks' gestation. IUGR fetuses had lower umbilical vein (P = .004) and pulmonary blood flow (P = .01) and higher superior vena caval flow (P < .0001) by MRI. IUGR fetuses had asymmetric growth but smaller brains than normal fetuses (P < .0001). Newborns with IUGR also had smaller brains with otherwise essentially normal findings on MRI. Vessel T2s, oxygen delivery, oxygen consumption, middle cerebral artery pulsatility index, and cerebroplacental ratio were all significantly lower in IUGR fetuses, whereas there was no significant difference in umbilical artery pulsatility index. IUGR score correlated positively with superior vena caval flow and inversely with oxygen delivery, oxygen consumption, umbilical vein T2, and cerebroplacental ratio. Receiver-operating characteristic curves revealed equivalent performance of MRI and Doppler techniques in identifying IUGR that was defined based on postnatal parameters with superior vena caval flow area under the curve of 0.94 (95% confidence interval, 0.87-1.00) vs a cerebroplacental ratio area under the curve of 0.80 (95% confidence interval, 0.64-0.97).
MRI revealed the expected circulatory redistribution in response to hypoxia in IUGR fetuses. The reduced oxygen delivery in IUGR fetuses indicated impaired placental oxygen transport, whereas reduced oxygen consumption presumably reflected metabolic adaptation to diminished substrate delivery, resulting in slower fetal growth. Despite brain sparing, placental insufficiency limits fetal brain growth. Superior vena caval flow and umbilical vein T2 by MRI may be useful new markers of late-onset IUGR.
迟发型宫内生长受限（IUGR）是由于胎盘未能向快速生长的晚期胎儿提供足够的营养和氧气而导致的。目前监测方法的局限性需要额外的技术来更准确地诊断宫内 IUGR。新的磁共振成像（MRI）技术现在提供了一种用于胎儿血液动力学评估的非侵入性技术，这可能会为传统多普勒方法提供额外的信息。
本研究旨在使用新的 MRI 技术测量迟发型 IUGR 胎儿的血液动力学参数和大脑生长。
这是一项前瞻性观察性病例对照研究，旨在比较使用 MRI 测量主要胎儿血管和大脑成像的血流和 T2。指数化胎儿氧输送和消耗被计算出来。使用超声测量大脑中动脉和脐动脉搏动指数和脑胎盘比。以下 4 个参数中有 2 个或更多定义为 IUGR：（1）出生体重低于第 3 百分位或估计胎儿体重的百分位下降 20%；（2）30 周后最低脑胎盘比低于第 5 百分位；（3）体重指数 < 2.2；（4）胎盘组织学符合胎盘灌注不足的预设标准。在两组之间进行比较（学生 t 检验），并分析参数之间的相关性（皮尔逊相关）。使用受试者工作特征曲线比较 MRI 测量值与多普勒参数，以识别出生后标准定义的 IUGR（体重、胎盘组织学、体重指数）。
我们在 35 周时研究了 14 例 IUGR 和 26 例非 IUGR 胎儿。MRI 显示 IUGR 胎儿的脐静脉（P =.004）和肺血流量（P =.01）较低，而上腔静脉血流量（P <.0001）较高。IUGR 胎儿的生长不对称，但大脑比正常胎儿小（P <.0001）。新生儿 IUGR 也有较小的大脑，但在 MRI 上基本上有正常的发现。胎儿大脑中动脉搏动指数和脑胎盘比均显著降低，而脐动脉搏动指数无显著差异。IUGR 评分与上腔静脉血流量呈正相关，与氧输送、氧消耗、脐静脉 T2 和脑胎盘比呈负相关。受试者工作特征曲线显示，MRI 和多普勒技术在识别基于产后参数定义的 IUGR 方面具有等效性能，上腔静脉面积的曲线下面积为 0.94（95%置信区间，0.87-1.00），而脑胎盘比的曲线下面积为 0.80（95%置信区间，0.64-0.97）。
MRI 显示了 IUGR 胎儿对缺氧的预期循环重新分布。IUGR 胎儿的氧输送减少表明胎盘氧输送受损，而氧消耗减少可能反映了代谢适应底物输送减少，导致胎儿生长缓慢。尽管大脑得到了保护，但胎盘不足限制了胎儿大脑的生长。上腔静脉流量和 MRI 测量的脐静脉 T2 可能是迟发型 IUGR 的新的有用标志物。
