I'm struggling with filth as well, only because you've given us practically no context for what it might mean -- billy guessed abortion (based on the labor line), it could be a cancer, it could be talking about any metaphorical malady (like grief or love). Aside from the title and the last line mentioning it, there are no details given that will allow it to have the emotional resonance you want. If its a product of rape, for instance, and the violence of the surgery is meant to both undo and parallel the attack, then it would help to allude to the original event somewhat (this is all just guesswork of course). Other than that nit, it was a good read
PS. If you can, try your hand at giving some of the others a bit of feedback. If you already have, thanks, can you do some more?