The speaker in this poem might be bitter about having a child, but the sounds in her writing would be pleasing to a child's ear, as riddles often are. We could imagine a mother reading this aloud to her newborn child, the words slipping over her tongue in their smooth and upbeat rhythm. There's no rhyme scheme, but lines like "I'm a riddle in nine syllables" and "A melon strolling on two tendrils" are fun to say. And there are delightful moments of alliteration ("two tendrils," "Money's new-minted," and "cow in calf"), assonance ("riddle […] syllables" and "ivory, fine"), and consonance ("melon strolling" and "yeasty rising") that add music to the lines.
Despite the fun and flow of this writing, though, there are a couple places that catch—that show us that, hey, all is not well in this poem. For example, the word "ponderous" weighs heavy on our tongue, slowing us down much as a pregnant woman is slowed by her weight. The word "fat" sticks out in line six as more abrupt than all the surrounding sounds.
So even though this poem is fun to read aloud, parts of it are just as jerky and awkward as a pregnant woman's movement would be. That's kind of the point. We're not meant to enjoy ourselves here, but to ponder the heavy burden our speaker is bearing.