Both of Edith's parents were dead by the time she had her baby; her father died when she was very little. Even if they were still alive, I don't think her parents could do much, if anything, to delay her giving birth. Also, I doubt there's much difference from 17 right after turning 18, so any risks there might have been would still be there.

I know this is a late comment, but I wanna say that death by childbirth is really, really, really, really rare, which supports my theory that the curse is still there. She mentioned if she died before she could tell her son the stories.