Final answer:
The hormone that remains elevated in the immediate after-birth period of a breastfeeding woman is prolactin, which is crucial for the stimulation and continuation of milk production.
Step-by-step explanation:
The hormone that remains elevated in the immediate after-birth period of the breastfeeding woman is prolactin. After childbirth, the baseline prolactin level drops sharply, but it is restored for a 1-hour spike during each feeding to stimulate the production of milk for the next feeding. While estrogen and progesterone do increase slightly with each prolactin spike, it is the elevated prolactin levels that are crucial for continued lactation. Additionally, after the placenta is expelled post-childbirth, the inhibition of prolactin-mediated milk synthesis by estrogen, progesterone, and other placental hormones is lifted, allowing milk production to commence.