Green’s Dictionary of Slang

(US/UK/W.I.) a general term of abuse.

1981		(con. 1963) P. Conroy Lords of Discipline 191: Where do you think you’re going, afterbirths?
1995		Francis-Jackson Official Dancehall Dict. 1: After-Birth a rude remark embodying total contempt to whomever it is directed.
2004		N. ‘Razor’ Smith Few Kind Words and a Loaded Gun 52: Now, you fucking poor excuse for an afterbirth, when I say ‘go’, you will double your stinking little body over to that desk.