I'm a riddle in nine syllables,
An elephant, a ponderous house,
A melon strolling on two tendrils.
O red fruit, ivory, fine timbers!
This loaf's big with its yeasty rising.
Money's new-minted in this fat purse.
I'm a means, a stage, a cow in calf.
Red suggests the flesh of the baby. Ivory suggests the bones, and the fine timbers suggest the growing limbs. Compare also the expression “fruit of her loins.” 
 Don’t read too much into ‘O’. It simply emphasizes the sense of exhibition referring to the baby.
Metaphors