The life of twins is often considered a "life as a couple" because of the deep bond that characterizes them, the mutual dependence, the communication that, especially among children, shows itself through a kind of language only they can interpret.
These characteristics raise questions about their relationship during pregnancy: what are the peculiarities of the relational life between two (or more) occupants sharing the same womb from the earliest stages of implantation?
Since, objectively, from the physical standpoint, the intrauterine life of twins is more problematic, will it not also be so on the psychic level which, as Freud says, derives from the physical-bodily level, since "everything that is psychic was first somatic"?
Fetal neurophysiology and studies carried out with ultrasound probes (which allow certain peculiar aspects of twins' development in utero to be visualized), as well as psychoanalytic work carried out with pairs of twins, make it possible to put forward hypotheses, often contradictory, on this subject. It is reasonable to hypothesize that there is a difference between identical and fraternal twins as regards their ability to perceive and register the impulses coming from the maternal body during pregnancy. The former are, in fact, the product of a single embryo that divides at an early stage, and thus share the same genetic makeup; each is a mirror of the other through phylogenetic and ontogenetic inheritance. For some, this reality is synonymous with easy coexistence; others argue, on the contrary, that the later the differentiation occurs, the greater the relational difficulties. In support of this thesis, they point to the extreme difficulty of coexistence that can develop in certain cases of monozygotic, monochorionic, monoamniotic pregnancy (in which, that is, the twins must survive in the same amniotic sac, sharing a single placenta), as an example. This is the feared "twin-to-twin transfusion syndrome", which amounts to an "extreme struggle" between the twins to secure the conditions indispensable for survival. This situation thus suggests that their relationship is influenced by factors relating to their chances of survival, more than by the similarity of their genetic makeup.
But what happens with fraternal twins, who do not share the same genetic makeup (they may be the result of two acts of intercourse, even with two different men), who develop in two separate amniotic sacs with two different placentas? Is it reasonable to hypothesize that always being together in a confined space, one that, as the pregnancy progresses, increasingly limits their ability to move, leads them to form a relationship marked by the development of a greater natural aggression, indispensable for their own survival?
This hypothesis would start from the assumption that each twin recognizes the other as different from himself. But is this really the case?
As emerges from the evidence gathered through psychoanalytic work, the fetus does not perceive itself as a subject in its own right, but as part of the maternal body. Based on this assumption, then, each twin should perceive the other as a "maternal attribute" that limits space and makes survival more difficult. If every embryo/fetus experiences this natural aggression toward the mother, there is no reason why the twin, experienced as part of the mother, should be exempt from it. Nor can the deep bond between twins after birth disprove this, since, at the unconscious level, behind the "too much" of any display of affection lies its opposite. So one should not rule out a profound intrauterine aggression between twins, which, in most cases, in life after birth, is replaced and/or masked by a solid bond of love.