**Core Concept**
Estrogen and progesterone levels fluctuate during the menstrual cycle, influencing various physiological processes. However, not all hormones exhibit this variation. Understanding the hormonal dynamics of the menstrual cycle is crucial for diagnosing and managing related disorders.

**Why the Correct Answer is Right**
The hormone with no change in levels during the menstrual cycle is testosterone. Testosterone is produced by the ovaries and adrenal glands, and its production is not significantly influenced by the menstrual cycle. Unlike estrogen and progesterone, testosterone levels remain relatively stable throughout the cycle, with minimal fluctuations.

**Why Each Wrong Option is Incorrect**
**Option B:** Estrogen levels do change significantly during the menstrual cycle, peaking in the luteal phase. This is due to the conversion of androgens to estrogens by the enzyme aromatase in the ovaries.
**Option C:** Progesterone levels also fluctuate during the menstrual cycle, rising after ovulation and remaining elevated in the luteal phase. This hormone is crucial for preparing the uterus for potential pregnancy.
**Option D:** FSH (Follicle-Stimulating Hormone) levels change during the menstrual cycle, peaking in the follicular phase to stimulate follicular growth and estrogen production.

**Clinical Pearl / High-Yield Fact**
It's essential to note that while testosterone levels remain relatively stable, the ratio of testosterone to estrogen can change during the menstrual cycle, influencing various physiological and pathological processes.

**Correct Answer:** D. FSH (Follicle-Stimulating Hormone) levels change during the menstrual cycle, peaking in the follicular phase to stimulate follicular growth and estrogen production.