## **Core Concept**
Ovulation is a critical event in the menstrual cycle where a mature ovum is released from the ovarian follicle into the fallopian tube. It is primarily regulated by a surge in luteinizing hormone (LH) levels. Various methods can help determine if ovulation has occurred.

## **Why the Correct Answer is Right**
The correct answer, **B. Basal body temperature (BBT) increase**, is a commonly used indicator of ovulation. After ovulation, under the influence of progesterone produced by the corpus luteum, there is a noticeable increase in basal body temperature. This increase is usually by 0.4-1.0°C and is sustained until the onset of menstruation. Progesterone has a thermogenic effect, leading to this rise in BBT.

## **Why Each Wrong Option is Incorrect**
- **Option A:** While a decrease in estrogen levels does occur after ovulation, directly measuring estrogen levels is not a practical method for confirming ovulation compared to other indicators.
- **Option C:** An increase in FSH (Follicle-Stimulating Hormone) actually occurs before ovulation to stimulate follicular growth and is not an indicator of ovulation itself but rather a precursor.
- **Option D:** A decrease in LH levels is not a reliable indicator of ovulation; rather, it is the surge in LH that triggers ovulation.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the increase in basal body temperature occurs **after** ovulation has taken place. Therefore, tracking BBT can help predict future fertility but does not confirm ovulation in real-time. It is a retrospective indicator.

## **Correct Answer:** . Basal body temperature increase