In keeping with its central theme of alienation and awakening, the tone of the poem is at first objective and detached, then, in the last two stanzas, more involved and appreciative. The poem is about a mother's reaction to her new baby, but, contrary to expectations, it does not express instant love and bonding. With stark honesty, Plath is saying that she doesn't immediately feel strong emotion for her child - the only mention of love is in the first line, and it refers to the act that created the child, not what she feels for the child now that it is born. Also, in the third stanza, she says, "I'm no more your mother than the cloud that distills a mirror".
The tone changes in the last two stanzas, when the baby cries. The mother responds by "stumbl(ing) from bed" to feed it, and then hears the baby's sated cries in a much more positive light, as a "handful of notes; the clear vowels rise like balloons". Through her use of tone, Plath appears to be illustrating that it is the baby's need, as expressed in its cry, that spurs a mother to involvement and the beginning of appreciation and emotional attachment.