Ml. Denbow et al., Placental angioarchitecture in monochorionic twin pregnancies: Relationship to fetal growth, fetofetal transfusion syndrome, and pregnancy outcome, AM J OBST G, 182(2), 2000, pp. 417-426
OBJECTIVE: We sought to correlate placental vasculature with fetal growth a
nd outcome in monochorionic twins.
STUDY DESIGN: Eighty-two patients with consecutive monochorionic pregnancie
s underwent biweekly ultrasonography for determination of fetal growth and
well-being. After delivery, blinded placental injection studies delineated
vascular anastomoses and territory share. Degree of balance in arteriovenou
s anastomoses equaled the number of arteriovenous anastomoses in one direct
ion minus the number in the other.
RESULTS: Pregnancies affected by fetofetal transfusion syndrome (n = 21) ha
d numbers of arteriovenous and venovenous anastomoses that were similar to
those in pregnancies without fetofetal transfusion syndrome but fewer arter
ioarterial anastomoses (P < .0001). Fetofetal transfusion syndrome occurred
in 78% of pregnancies with 21 arteriovenous and no arterioarterial anastom
oses. Birth weight discordancy correlated with placental territory discorda
ncy (P < .0001) and the degree of balance in arteriovenous anastomoses (P =
.004). The larger placental share twin had a greater growth velocity than
its smaller placental share cotwin (P = .008) for all but one anastomotic p
attern. Where arteriovenous anastomoses were aligned with the net venous ou
tflow to the fetus with the smaller territory, co-twins had similar birth w
eights and growth velocities irrespective of placental share. Fetal surviva
l was higher in pregnancies with an arterioarterial anastomosis (P = .01) b
ut lower with a venovenous anastomosis (P = .01). Survival of both fetuses
was inversely associated with birth weight discordancy (P < .0001).
CONCLUSION: Although interrelationships among the various types of anastomo
ses are complex, our data suggest that the placental territory share and th
e pattern of arteriovenous anastomoses influence fetal growth, that arterio
arterial anastomoses protect against fetofetal transfusion syndrome, and th
at venovenous anastomoses reduce perinatal survival.