Monochorionic Twins and Twin–Twin Transfusion Syndrome: The Protective Role of Arterio-arterial Anastomoses

Unidirectional arterio-venous (AV) anastomoses often result in twin-twin transfusion syndrome (TTTS). Additional oppositely directed anastomoses may compensate for the circulatory imbalance and either prevent, delay the onset, or moderate the severity of TTTS. Intuitively, higher pressure gradient,...

Full description

Saved in:

Bibliographic Details
Published in:	Placenta (Eastbourne) 2002-02, Vol.23 (2-3), p.201-209
Main Authors:	Umur, A., van Gemert, M.J.C., Nikkels, P.G.J., Ross, M.G.
Format:	Article
Language:	eng
Subjects:	Adult Amniotic Fluid - physiology Arterio-Arterial Fistula - physiopathology Biological and medical sciences Female Fetal Blood - physiology Fetofetal Transfusion - physiopathology Fetofetal Transfusion - prevention & control Fractals Fundamental and applied biological sciences. Psychology Hemodynamics - physiology Humans Microcirculation - physiology Models, Biological Mother. Fetoplacental unit. Mammary gland. Milk Nonlinear Dynamics Placenta - blood supply Pregnancy Pregnancy. Parturition. Lactation Twins, Monozygotic Vertebrates: reproduction
Online Access:	Get full text
Tags:	Add Tag No Tags, Be the first to tag this record!

Description
Summary:	Unidirectional arterio-venous (AV) anastomoses often result in twin-twin transfusion syndrome (TTTS). Additional oppositely directed anastomoses may compensate for the circulatory imbalance and either prevent, delay the onset, or moderate the severity of TTTS. Intuitively, higher pressure gradient, oppositely-directed AV anastomoses (indicated as VA) would be expected to compensate better for TTTS than lower pressure gradient arterio-arterial (AA) anastomoses. However, clinical evidence suggests AA anastomoses compensate more efficaciously, because virtually all non-TTTS monochorionic twin placentas have AAs (84 per cent), contrary to TTTS placentas, where only 30 per cent have an AA. We sought to explain this observation by comparing the capabilities of various size VA and AA anastomoses to compensate for the effects of the primary AV. As study design we used a previously developed mathematical computer model of TTTS to determine ranges of anastomotic vascular resistances which cause varying fetal and amniotic fluid discordances. Anastomotic resistances were related with the radii of their feeding vessels, using fractal geometry modelling to mimic the placental vascular tree, and various assumptions regarding arterial blood flow. The results were as follows. An AA anastomosis of equal size as the feeding artery of an AV or VA has a significantly smaller resistance. The primary AV anastomosis may be compensated by both VA as well as AA anastomoses. However, VA transfusion adequately compensates AV flow only for a small range of VA to AV vascular radius ratios. In contrast, AA transfusion compensates the AV flow for a much wider range of AA to AV vascular radius ratios. In conclusion, the wider range of AA than VA radii for adequate compensation of the AV explains the finding that an AA protects more frequently than a VA of similar size against the manifestations of TTTS. These results may possibly allow future risk stratification of monochorionic twins by non-invasive sonographic assessment of the size and type of anastomoses.
ISSN:	0143-4004 1532-3102