Rainbow Baby???

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Is a rainbow baby a baby that is BORN after Mc... or a PREGNANCY after Mc? Ive had 3 Mc total, and I keep seeing people post positive tests saying they finally got their rainbow baby.... but all I can think is how do you know this is your rainbow baby??? I know I may be a little bitter and hesitant after having 3.... but when I see that I just get sad and think... but what if it’s NOT... help me understand the term better please? Currently 6+2 and I don’t know if that means I have a rainbow baby or I’m praying it will be....