## Core Concept
The ovarian cycle is regulated by a complex interplay of hormones, including luteinizing hormone (LH) and follicle-stimulating hormone (FSH), which are secreted by the anterior pituitary gland. The surge in LH levels plays a critical role in ovulation. This surge is primarily triggered by a positive feedback mechanism involving estrogen.

## Why the Correct Answer is Right
The correct answer, , involves the positive feedback effect of estrogen on the secretion of LH. As the follicular phase progresses, the growing follicles produce increasing amounts of estrogen. Once estrogen levels reach a threshold, they exert a positive feedback effect on the hypothalamus and pituitary gland, leading to a significant increase in the secretion of LH. This LH surge is essential for ovulation, causing the dominant follicle to release an oocyte.

## Why Each Wrong Option is Incorrect
* **Option A:** - This option is incorrect because the negative feedback of estrogen and progesterone primarily affects the secretion of FSH and to some extent LH, but it does not explain the surge in LH levels.
* **Option B:** - This option is incorrect as it does not accurately describe the primary mechanism behind the LH surge during the ovarian cycle.
* **Option C:** - Although FSH levels do increase during the early follicular phase, the surge in LH is not directly caused by increased FSH levels but by the positive feedback of estrogen.

## Clinical Pearl / High-Yield Fact
A key clinical pearl is that the LH surge is what triggers ovulation. Understanding the regulation of the LH surge is crucial for diagnosing and managing infertility and for the timing of procedures like intrauterine insemination (IUI) or in vitro fertilization (IVF).

## Correct Answer Line
**Correct Answer: D. Positive feedback effect of estrogen.**