**Question:** The laboratory report shows values of gonadotropin and ovarian hormones in the blood sample taken on day 20 of the menstrual cycle of a young woman. Whether her cycle was ovulatory or not may be validly assessed by the serum level of:

**Core Concept:**
Gonadotropins are hormones secreted by the anterior pituitary gland, and they play a crucial role in regulating the menstrual cycle and ovarian function. Ovarian hormones include estrogen and progesterone, which are produced by the ovaries in response to gonadotropin stimulation. In the context of the menstrual cycle, the luteal phase is characterized by high levels of estrogen and progesterone production.

**Why the Correct Answer is Right:**

In a typical menstrual cycle, the luteinizing hormone (LH) surge occurs around day 14, leading to ovulation. Ovulation triggers a rapid increase in both LH and follicle-stimulating hormone (FSH) levels. Ovulation occurs when the LH surge is followed by a FSH surge.

**Why Each Wrong Option is Incorrect:**

Option A (FSH): While FSH is essential for the initiation and growth of ovarian follicles, it is not the primary indicator of ovulation. Ovulation is more accurately assessed by the LH surge.

Option B (Estrogen): Estrogen levels rise during the luteal phase of the menstrual cycle, not on day 20 when the question is asked. Assessing ovulation based on estrogen levels would not accurately determine if ovulation has occurred.

Option C (Progesterone): Progesterone levels rise during the luteal phase, following ovulation. Assessing ovulation based on progesterone levels on day 20 would be incorrect.

Option D (LH): While LH levels increase on day 20, they do not indicate ovulation. Ovulation is determined by the LH surge preceding the FSH surge.

**Clinical Pearl:**

To accurately assess ovulation in a woman's menstrual cycle, consider evaluating the LH surge preceding the FSH surge on day 14, not individual hormone levels on day 20. This method allows for a more precise determination of ovulation, which is crucial for understanding fertility, diagnosing reproductive disorders, and planning fertility treatments.