**Core Concept**
Ovulation is a critical phase in the menstrual cycle where the dominant follicle releases an ovum from the ovarian follicle, marking the beginning of a potential pregnancy. This process is regulated by a complex interplay of hormonal changes, primarily involving the pituitary gland and the hypothalamus.

**Why the Correct Answer is Right**
Ovulation can be diagnosed through various methods that detect the physiological changes associated with this event. One common method is the basal body temperature (BBT) method, which relies on the slight increase in BBT that occurs after ovulation due to the production of progesterone by the corpus luteum. Another method is the luteinizing hormone (LH) surge, which can be detected using urinary LH kits or blood tests. Additionally, ultrasound examination can visualize the follicular maturation and rupture.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a method of diagnosing ovulation.
**Option B:** This option is incorrect because it is not a commonly used method for diagnosing ovulation.
**Option C:** This option is incorrect because it is a method of diagnosing ovulation, specifically through the detection of LH surge.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that ovulation is a critical window for fertility, and its timing can be influenced by various factors, including hormonal imbalances, polycystic ovary syndrome (PCOS), and age-related decline in ovarian reserve. Understanding the physiological changes associated with ovulation is essential for managing fertility issues and preventing complications.

**Correct Answer: D.**