Placental sharing, birthweight discordance, and vascular anastomoses in monochorionic diamniotic twin placentas.
OBJECTIVE
The purpose of this study was to examine the relationship between placental territory and birthweight discordance and vascular anastomoses in monochorionic diamniotic twin placentas from pregnancies that were not complicated by twin-to-twin transfusion syndrome with 2 liveborn twins.


METHODS
Placentas originated from a prospective follow-up study of monochorionic diamniotic twins included in the first trimester. After injection with dyed barium sulphate, a digital x-ray angiography and high-resolution digital photograph were taken. The 2 venous territories were delineated on the angiogram. The diameter of each arterioarterial anastomosis and of each vein that participated in an arteriovenous anastomosis was measured on the digital photograph. Net transfusion over the arteriovenous anastomoses was calculated as the difference between the total venous diameters of the 2 placental parts.


RESULTS
One hundred placentas were analyzed. Birthweight discordance increased with placental territory discordance (P < .0001). Arterioarterial diameter (P < .01), net arteriovenous transfusion (P < .001), and total anastomotic diameter (P < .01) increased with placental territory discordance. On the other hand, birthweight discordance for a given placental territory discordance decreased with increasing arterioarterial diameter (P < .01), net arteriovenous transfusion (P < .001), and total anastomotic diameter (P < .01).


CONCLUSIONS
In unequally shared placentas, the 2 fetal circulations are more tightly linked than in equally shared placentas, which may reduce the birthweight discordance for a given placental territory discordance.
Department of Obstetrics and Gynecology, University Hospital, Leuven, Belgium.
Liesbeth
L
Lewi
Mieke
M
Cannie
Isaac
I
Blickstein
Jacques
J
Jani
Agnes
A
Huber
Kurt
K
Hecher
Steven
S
Dymarkowski
Eduard
E
Gratacós
Paul
P
Lewi
Jan
J
Deprest
D000792:Angiography; D001163:Arteriovenous Anastomosis / Q000000981:diagnostic imaging* / Q000502:physiology; D001724:Birth Weight; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D010920:Placenta / Q000098:blood supply* / Q000502:physiology; D021041:Placental Circulation / Q000502:physiology*; D011247:Pregnancy; D014430:Twins, Monozygotic / Q000502:physiology*