This poem admits it, right off the bat: it's a riddle. Then it presents us with several different metaphors to help us find the solution. We hear about an elephant, a house, a couple of different kinds of fruit, bread rising, newness, fatness, and a cow in calf. By this point in the poem, we figure out that the riddle is about a pregnant woman, thanks to all the images of round things. But these ways of describing a pregnant woman aren't necessarily the images of expecting that we've come to expect—they're less than glowing and even a little bitter.
Then, in the last two lines, we start to get even more of a feeling that the speaker is uneasy about this whole pregnancy thing. She describes eating a bag of apples—which we can imagine filling her stomach in the shape of this pregnancy—as if she's done something wrong. She seems to feel stuck in this wild and disproportionate situation and body, and there's no getting off this train.