The Vanishing Twin Syndrome is rather a phenomenon of the ultrasound age; this phenomenon is now being detected, earlier, without the benefit of detecting a twin pregnancy very early on in a pregnancy it would have gone quite unnoticed!
This is particularly true since the pregnancy complications of the vanishing twin syndrome is chiefly a feature of the first trimester, where, for reasons not fully understood, one or more fetuses of a multiple pregnancy may be reabsorbed by the body.
What is most commonly understood as being the reasons behind the vanishing twin syndrome is, that one or more of the fetuses of a multiple pregnancy would have had some congenital defects incompatible with being carried to term or for some reason were not receiving enough nutrition and so got reabsorbed into the body.
Sometimes it is an improperly placed placenta that causes this phenomenon, or it could happen as a result of a blighted ovum where the zygote did not develop beyond the very early stages.
Usually there are no complications of the vanishing twin syndrome and a woman does not even realize that such re-absorption of one fetus is taking place. However, in some cases mild cramping and some amount of bleeding may be experienced.
Another possible but seldom occurring complication of the vanishing twin syndrome could be that the fetus that dies could remain in the uterus becoming desiccated and compressed by the surviving baby or babies.
This could then be delivered in a flattened stage at the time of delivery, at whatever stage of development was reached by the fetus before death. Such a remnant of the dead twin, also known as Fetus Papyraceus could cause serious complication at the time of delivery if it blocks the cervix, obstructing the passage of the surviving baby.
Sometimes one of the babies of a multiple pregnancy could die a little later in the pregnancy and then there could be several rather serious complications of the vanishing twin syndrome. If the event occurs in the second or third trimester, there could be several problems such as a premature labor, infections due to the vanished twin, and even hemorrhage.
It is also thought that complications of a vanishing twin syndrome could persist for the surviving twin in later life as well; wherein the ‘twinless twin’ may experience emotions such as confusion, guilt, loss, because they may be negatively impacted by the loss of their twin.