It's all but impossible to write a poem about pregnancy and not tackle the theme of women and femininity head on. That's just what Plath does in "Metaphors." In her slew of comparisons, she paints a picture of what it means to be an expectant mother in her day and age, and let Shmoop tell you: that picture? It ain't pretty.
The metaphors in this poem show that the speaker feels as if, as a pregnant woman, she's become a valued commodity rather than a human being.
The references to fruit in this poem connect the speaker to the biblical first woman, Eve, and her perceived sin of eating the forbidden fruit.