**Core Concept**
The corpus luteum is a temporary endocrine structure in the female ovaries that plays a crucial role in the menstrual cycle and early pregnancy. Its primary function is to produce progesterone, which prepares the uterine lining for implantation of a fertilized egg.

**Why the Correct Answer is Right**
The corpus luteum forms after ovulation, when the ruptured follicle in the ovary transforms into a corpus luteum. This structure is highly vascularized and produces high levels of progesterone, which maintains the endometrial proliferation and differentiation necessary for implantation. The peak progesterone production by the corpus luteum occurs around 7-10 days after ovulation, preparing the uterus for potential implantation of a fertilized egg.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the corpus luteum's function is not limited to the menstrual phase, but it is also crucial for early pregnancy. **Option B:** This option is incorrect because the corpus luteum's function is not limited to estrogen production, but it is primarily responsible for progesterone production. **Option C:** This option is incorrect because the corpus luteum's function is not limited to the luteal phase, but it is also crucial for early pregnancy.

**Clinical Pearl / High-Yield Fact**
The corpus luteum's function is critical for early pregnancy, and its failure to produce adequate progesterone can lead to luteal phase defect, resulting in recurrent miscarriages.

**Correct Answer: C. 7-10 days after ovulation**