When a couple goes through the painful experience of losing a child (already born, or in an advanced stage of pregnancy) and sinks into a state of grief, they often believe that conceiving another child right away is the best way to start living again.
Faced with the suffering that follows such a trauma, and the unbearable, ominous feeling of not being able to raise (or have) a child, conceiving another leads the couple to look forward without being overwhelmed by what happened, but it doesn't help them work through the grief, that is, to withdraw the emotional investment from the child who is no longer there in order to reinvest that affection in one who will be.
This doesn't mean forgetting the lost child or no longer feeling affection for them, but managing to accept their death; otherwise, the new arrival will exist only as their substitute and will be burdened, from the very moment of conception, with the parents' unresolved issues, which will inevitably make their life difficult and painful.
It is easy, in fact, for a child carrying the conceptional identity* of a «replacement child» to develop psychopathological problems, linked to not feeling loved for who they are but only because they are standing in for the other child, to being compared to a sibling with unattainable, idealized qualities, and to feeling guilty, as though they had caused the other child's death, since if it hadn't happened, they themselves wouldn't exist.
For parents who have lost a child and are thinking about conceiving another, psychotherapy can be valuable help in fostering the distinction between the child who is gone and the one who is to come, as well as in speeding up the work of mourning.
If this working-through doesn't happen deep within the parents, the future child will end up being the other one's substitute, as happens in certain situations where they are given the same name, or their birth «coincidentally» falls on a date significant for the child who was lost.
Even though a «replacement child» has a more difficult start in life because of the context in which they were conceived, one that could disturb their development, there is no identifiable syndrome linked to this situation. Depending on the child's own psychic makeup and on the intensity and persistence of the atmosphere of grief surrounding them, their development can turn out to be entirely normal.
It's easy to predict, however, that this child will face greater difficulty asserting their own identity, since they were not conceived for themselves but to fill the void left by someone else, and greater difficulty getting through the various stages of separation, both in childhood and during adolescence, needed to achieve independence. Indeed, after the loss of a child, parents, who inevitably feel guilt even when the loss happened through no fault of their own, tend to become overprotective and stifling, as if trying to prevent the tragedy from repeating itself.
* Conceptional identity is the set of characteristics related to the circumstances in which a child is conceived.