An oophorectomy is the surgical removal of an ovary. Bilateral oophorectomies, in which both ovaries are removed, result in immediate menopause—often with intense symptoms—for premenopausal or perimenopausal women, as their bodies can no longer produce estrogen. A unilateral oophorectomy, by contrast, does not lead to instant menopause, as one ovary remains and can continue estrogen production.