A 51-year-old woman presents to the nurse practitioner with a chief complaint of "hot flashes." She describes the following symptoms: perspiration, flushing, chills, clamminess, anxiety, and occasional heart palpitations. Which of the following is the first-line treatment recommended by the American College of Obstetricians and Gynecologists (ACOG)?

Choice A reason: This is correct. Systemic estrogen therapy is the first-line treatment for moderate to severe vasomotor symptoms in perimenopausal and postmenopausal women. It effectively reduces hot flashes and associated symptoms. Choice B reason: Clonidine, an alpha-2 adrenergic agonist, may help with vasomotor symptoms but is less effective and not considered first-line. Choice C reason: Gabapentin can reduce hot flashes, especially in women who cannot take hormone therapy, but it is second-line. Choice D reason: Ospemifene is used for dyspareunia related to vulvovaginal atrophy and does not treat vasomotor symptoms.