## Core Concept
Steroidogenesis in the corpus luteum is crucial for maintaining early pregnancy by producing progesterone. This process involves the conversion of cholesterol into steroid hormones, a pathway that is dependent on specific enzymes and precursors. Luteinizing hormone (LH) plays a pivotal role in this process.

## Why the Correct Answer is Right
The correct answer, **LH (Luteinizing Hormone)**, is essential for adequate steroidogenesis in the corpus luteum. LH binds to LH receptors on the corpus luteum, stimulating the production of progesterone through a cascade that involves the increase of intracellular cyclic AMP (cAMP), activation of protein kinase A (PKA), and ultimately, the transcription of genes involved in steroidogenesis, including the steroidogenic acute regulatory protein (StAR) which is crucial for the transport of cholesterol into the mitochondria. This process is vital for the production of progesterone, necessary for preparing and maintaining the uterus for a fertilized egg.

## Why Each Wrong Option is Incorrect
- **Option A: FSH (Follicle-Stimulating Hormone)** is primarily involved in the growth and maturation of ovarian follicles and has a lesser role in the maintenance of the corpus luteum.
- **Option B: Prolactin** can actually inhibit reproductive functions, including GnRH secretion, and at high levels, can interfere with luteal function but is not essential for steroidogenesis in the corpus luteum.
- **Option D: Estrogen** is produced by the corpus luteum but is not the primary hormone responsible for stimulating steroidogenesis within it.

## Clinical Pearl / High-Yield Fact
A key clinical point to remember is that the corpus luteum is functionally dependent on LH. In early pregnancy, before the placental production of human chorionic gonadotropin (hCG) takes over, any decrease in LH levels can lead to inadequate progesterone production and potentially threaten the pregnancy.

## Correct Answer Line
**Correct Answer: C. LH.**