A rainbow baby is a term used to describe a child born to a parent or couple who have previously experienced miscarriage, stillbirth, neonatal loss, or the loss of an infant.
The birth of a rainbow baby can be a bittersweet experience for parents who are overjoyed by the birth of their child, while still mourning the loss of a child who has passed away. The use of this term is generally intended to reflect this tension.
FertilitySmarts explains Rainbow Baby
Rainbow baby is a term that is used to express the joy that has or will come with a successful pregnancy and delivery while remembering any previous loss. It is frequently used in trying to conceive (TTC) forums and infertility or miscarriage and loss blogs.
The term is inspired by the appearance of a rainbow in nature. Much like a rainbow appearing after a dark storm, the birth of a rainbow baby brings light and joy after enduring the hardship of losing a child. This new joy does not negate the experience of previous loss, but rather the loss and new birth co-exist like a rainbow in a dark sky.
To some, this term is a way to communicate to others that they have experienced previous loss without providing additional detail that may be personal or sensitive. It may be easier to say they are hoping for their rainbow baby rather than to state outright that they have experienced loss, particularly in an online setting.
Alternatively, others do not feel that this alternative term is appropriate or representative of their traumatic experience.