Money's new-minted in this fat purse. (6)
The word fat is used to refer to a purse, but since purse is a metaphor for our pregnant speaker, this means that she considers herself to be fat. This is the most negative word we've seen used to describe the speaker's large size so far in this poem. But hey, at least she's getting straight to the point.
I'm a means, a stage, a cow in calf. (7)
Sometimes, mean people call large, ugly woman "cows." Jumping off from the negative word, "fat," in the prior line, we are starting to feel less and less positive about the abundant belly of our pregnant speaker. When she's a melon, or a ripe red fruit, we can see her large size as pretty, but thinking about her as a cow in calf is not quite flattering.