Caesura occurs in six places in "I, Being born a Woman and Distressed." Millay uses caesura in order to play with the rhythm of the poem and provide additional emphasis on certain ideas or phrases. Millay also uses caesura in conjunction with asyndeton in order to create dramatic tension.
In the first line of the poem, the speaker declares that she is a woman. The caesura created by the comma in line 1 slows down the reading here in order to emphasize the speaker's declaration. It creates a stressed beat on the word "I," forcefully asserting the speaker's presence in the poem. Sonnets are usually written in iambic pentameter, meaning readers would expect the poem's opening beat to be unstressed (da-DUM); that it is not foreshadows the subversion to come. Sonnets are also traditionally written from the point of view of a male speaker. "I, Being born a Woman and Distressed" has, of course, a female speaker, and the pause of the caesura also draws attention to this.
In line 4, the speaker goes on to describe her attraction to another individual. She is affected by their physical proximity to one another, which increases the beauty of this individual in her eyes. The caesura in the middle of line 4 again slows the reading of the poem, drawing attention to the speaker's attraction and emphasizing her lust for this individual.
Millay also uses caesura to resonate with the speaker's inner state of mind. In line 8, for example, the speaker describes the intensity of her lust, which leaves her "undone, possessed." Millay uses caesura with asyndeton to actually speed up the reading of the line by omitting any conjunctions. This speeding up of the line mirrors the speaker's agitated state of mind as her lust takes over her body.
In line 12, the speaker makes clear her contempt for the other individual, before reiterating her opinion. The clear caesura in the middle of the line draws attention to the speaker's intense feelings of "scorn." The extended pause in the middle of the line also creates a sense of suspense and hope. One might hope that the speaker will change her mind or moderate her feelings on the other individual. However, in the lines following the caesura, the speaker makes "plain" that her opinions will never, in fact, change.