Considerations on growth discordant twins.

Some considerations as to the pathophysiology of growth discordancy in twins are presented. Based on findings of Doppler flow measurements in growth discordant twins an alternative mechanism to that of twin-twin transfusion is presented which leads to a small stuck twin with an oligohydramnios and an oversized twin surrounded by a polyhydramnios. Based on feto-fetal interrelations the smaller fetus with an insufficient placental supply sends out growth-stimuli that finally result in increased growth of the other fetus with a normal placental function. Only in multiple pregnancies can such a signal have the effect of growth promotion on the fetus with normal supply. The result is being called Growth Factor Sequence, and in contrast to feto-fetal transfusion there is no difficulty to understand why the smaller fetus may have an enddiastolic block in the fetoplacental circulation. Thus, as long as feto-fetal transfusion is not proven, different pathomechanisms--like that of the Growth Factor Sequence--have to be taken into account in cases of discordant twins.