Like "Simile," this poem covers a range of comparisons to describe the baby that was growing inside of Sylvia Plath's womb at the time of writing. The sheer creative range of the various comparisons perhaps conveys the sense of wonder and amazement at what is happening inside of her and the baby that is growing into a little person. As such the poem's theme is the wonder of motherhood and how amazing it is: the growth of a tiny, microscopic cell into a fully-grown baby inside the mother's womb. The last line in particular is particularly poignant:
A clean slate, with your own face on.
The baby represents a new start, not weighed down by the history of its parents, and with its own identity, rather than inheriting the identity of its parents. We can see in this poem the love that Plath feels for her baby and her excitement at seeing what it will be like.
Before giving birth a baby , poem is about the pregnant women.
All which she describe is her feelings.