An ovulation predictor test identifies rising levels of which key reproductive hormone?

An ovulation predictor test is designed to detect the surge of luteinizing hormone (LH), which is crucial in the ovulatory process. During the menstrual cycle, a significant increase in LH levels indicates that ovulation is imminent, typically occurring 24 to 36 hours after this surge. The presence of LH is a reliable indicator of the body preparing to release an egg, making it the focal point for such tests.

While estradiol, FSH, and progesterone play important roles in the menstrual cycle and reproductive health, they do not directly indicate the timing of ovulation in the same way that LH does. Estradiol levels rise leading up to ovulation but do not result in the immediate trigger for ovulation itself. Follicle-stimulating hormone (FSH) is involved in the development of ovarian follicles but peaks earlier in the cycle than the ovulatory phase. Progesterone is primarily important after ovulation occurs, as it helps prepare the uterine lining for potential implantation of a fertilized egg. Therefore, the focus of ovulation predictor tests on LH is what makes it the correct answer.