## **Core Concept**
The rise in body temperature after ovulation is primarily due to the effect of a hormone that increases body temperature. This phenomenon is a well-known indicator of ovulation and is used in fertility awareness methods. The hormone responsible for this effect acts on the hypothalamus, which regulates body temperature.

## **Why the Correct Answer is Right**
The correct answer, **progesterone**, causes an increase in body temperature. After ovulation, the ruptured follicle in the ovary forms the corpus luteum, which secretes **progesterone**. Progesterone has a thermogenic effect, meaning it increases the body's temperature set point. This results in a noticeable rise in basal body temperature, typically by about 0.4 to 1.0 degree Fahrenheit (or 0.2 to 0.5 degree Celsius), which is sustained until the beginning of menstruation. This temperature shift is one of the body's natural indicators of ovulation.

## **Why Each Wrong Option is Incorrect**
- **Option A:** Estrogen does not cause a significant rise in body temperature post-ovulation. While estrogen levels do fluctuate throughout the menstrual cycle and estrogen can have various effects on the body, the post-ovulatory increase in body temperature is specifically attributed to progesterone.
- **Option B:** This option is not provided, but based on the context, any other hormone not directly linked to ovulation and thermogenesis would be incorrect.
- **Option D:** Without a specific option provided for D, we can infer that any other physiological reason or hormone not directly related to the action of progesterone on body temperature would be incorrect.

## **Clinical Pearl / High-Yield Fact**
A key clinical pearl is that the **biphasic pattern of basal body temperature** can be used as a simple, non-invasive method to confirm ovulation. The temperature increases after ovulation due to **progesterone** and remains elevated until menses. This method, while not highly precise for timing, can help in understanding the menstrual cycle and in family planning.

## **Correct Answer:** . Progesterone