Jaffe R, Jauniaux E, Hustin J
Department of Obstetrics and Gynecology, University of Rochester, NY 14642, USA.
Am J Obstet Gynecol. 1997 Mar;176(3):695-705. doi: 10.1016/s0002-9378(97)70572-6.
The classic theory of development of the uteroplacental and intervillous circulation determined that maternal blood enters the intervillous space in high-pressure streams from the early first trimester. This theory has recently been challenged and our hypothesis to be presented is that the intervillous circulation is not fully established until the end of the first trimester. Ex vivo studies of hysterectomy specimens have demonstrated that trophoblastic plugs obstruct blood flow into the intervillous space in early pregnancy and only at 12 to 13 weeks do these plugs become loose and allow for continuous maternal blood flow into the intervillous space. This concept is supported by many other experimental findings. In complicated early pregnancies the uteroplacental circulation demonstrates flow characteristics that are strikingly different from those of normal early pregnancies. In abnormal pregnancies increased flow within the intervillous space is demonstrated by color Doppler imaging. Our hypothesis supports other studies that have shown that the embryo favors an environment low in oxygen during early development and that oxygen levels in placental tissue are low in the early first trimester. The classic drawing of placental circulations is based on second- and third-trimester studies, and its applicability to the early first trimester should be revisited because we will show that new data support the hypothesis that the development of the early intervillous circulation is a progressive phenomenon.
子宫胎盘及绒毛间隙循环发育的经典理论认为，从妊娠早期开始，母体血液以高压血流的形式进入绒毛间隙。该理论最近受到了挑战，我们即将提出的假说是，绒毛间隙循环直到妊娠早期结束时才完全建立。对子宫切除标本的体外研究表明，滋养层栓在妊娠早期会阻碍血液流入绒毛间隙，只有在12至13周时这些栓才会松动，使母体血液持续流入绒毛间隙。这一概念得到了许多其他实验结果的支持。在复杂的早期妊娠中，子宫胎盘循环表现出与正常早期妊娠截然不同的血流特征。在异常妊娠中，彩色多普勒成像显示绒毛间隙内血流增加。我们的假说支持了其他研究，这些研究表明胚胎在早期发育过程中倾向于低氧环境，且在妊娠早期胎盘组织中的氧含量较低。胎盘循环的经典图示基于妊娠中期和晚期的研究，其对妊娠早期的适用性应重新审视，因为我们将表明新的数据支持早期绒毛间隙循环发育是一个渐进现象的假说。
