van Gemert M J, Kranenburg-Lakeman P, Milovanović Z, Vergroesen I, Boer K
Laser Centre, Academic Medical Centre, University of Amsterdam, The Netherlands.
Phys Med Biol. 2001 Mar;46(3):N57-63. doi: 10.1088/0031-9155/46/3/401.
Our objective was to appraise whether an increased amniotic fluid pressure by polyhydramnios can beneficially affect monochorionic twins that are haemodynamically connected by arterio-venous plus arterio-arterial placental anastomoses. We assessed the effects of polyhydramnios in monochorionic twin placentas, combining (a) data from previous in vitro placental perfusion experiments in singleton term placentas under simulated normal and increased amniotic fluid pressures with (b) logical deduction from observations made in monochorionic twins. Our hypothesis is that in monochorionic placentas, an increased amniotic fluid pressure increases the placental microvascular resistance but not the resistance of placental chorionic plate arteries. Hence, an increased amniotic fluid pressure increases the microvascular resistance of the joint cotyledon, the arterio-venous resistance, but not the arterioarterial resistance. This proposed mechanism reduces arterio-venous but not oppositely directed arterio-arterial transfusion. Therefore, reversal of the normal direction of net foeto-foetal transfusion may develop, which will reduce the circulatory imbalance that evolved between the monochorionic foetal twins. In contrast, in monochorionic twins connected by unidirectional or bidirectional arterio-venous anastomoses reversal of the normal direction of net foeto-foetal transfusion will not occur. In conclusion, reversal of the normal direction of net foeto-foetal transfusion, induced by polyhydramnios, is protective against the onset and severity of twin-twin transfusion syndrome in monochorionic twins connected by arterio-venous plus arterio-arterial anastomoses, but not by unidirectional or bidirectional arterio-venous anastomoses.
我们的目的是评估羊水过多导致的羊膜腔内压力升高是否能对通过动静脉加动脉-动脉胎盘吻合实现血流动力学连接的单绒毛膜双胎产生有益影响。我们评估了羊水过多在单绒毛膜双胎胎盘中的作用，将（a）先前在足月单胎胎盘模拟正常和升高羊水压力下进行的体外胎盘灌注实验数据与（b）从单绒毛膜双胎观察结果进行的逻辑推导相结合。我们的假设是，在单绒毛膜胎盘中，羊膜腔内压力升高会增加胎盘微血管阻力，但不会增加胎盘绒毛板动脉的阻力。因此，羊膜腔内压力升高会增加联合绒毛叶的微血管阻力、动静脉阻力，但不会增加动脉-动脉阻力。这种提出的机制会减少动静脉输血，但不会减少相反方向的动脉-动脉输血。因此，可能会出现正常胎儿-胎儿净输血方向的逆转，这将减少单绒毛膜双胎胎儿之间出现的循环失衡。相比之下，在通过单向或双向动静脉吻合连接的单绒毛膜双胎中，正常胎儿-胎儿净输血方向不会发生逆转。总之，羊水过多导致的正常胎儿-胎儿净输血方向逆转，对通过动静脉加动脉-动脉吻合连接的单绒毛膜双胎中双胎输血综合征的发生和严重程度具有保护作用，但对通过单向或双向动静脉吻合连接的单绒毛膜双胎则没有保护作用。
