Apparently, it is quite common in multiple pregnancies for one fetus to be 'absorbed' by the other one. Here is an excellent article about the causes and effects of the vanishing twin syndrome: http://americanpregnancy.org/multiples/vanishing-twin-syndrome/
This made me think about the psychological adjustment of the surviving twin. We all know how close twins, especially identical twins, are to each
other. Research have shown that twins feel each others' emotions, etc
etc, and if one should die, the remaining twin suffers more than when a non-twin sibling dies. But what about it if one twin dies invitro, like in the vanishing twin syndrome? Would
the survivor 'feel' the loss of the twin who died before birth, later in life?