Okay, let's tackle this question about what maintains the corpus luteum. The question is straightforward: "Corpus luteum is maintained by..." with options A, B, C, D. The correct answer is supposed to be hCG from the placenta, but I need to verify that.

First, the core concept here is the hormonal regulation of the corpus luteum. The corpus luteum forms after ovulation from the ruptured follicle. Its main function is to produce progesterone, which is crucial for maintaining the endometrium during the early stages of pregnancy. If the egg is fertilized, the placenta starts producing hCG, which takes over the role of maintaining the corpus luteum. If not, the corpus luteum degenerates after a few weeks.

So, the key here is understanding the transition from luteinizing hormone (LH) to hCG in sustaining the corpus luteum. During the menstrual cycle, the corpus luteum is initially maintained by LH. However, in pregnancy, the placenta secretes hCG, which has a similar structure to LH and can bind to the same receptors, thereby preventing the luteum from degenerating. This allows the corpus luteum to continue producing progesterone until the placenta can take over hormone production, which happens around the 10th week of pregnancy.

Now, looking at the incorrect options, they might include other hormones like FSH, estrogen, or progesterone. FSH is more involved in follicular development, not luteal phase. Estrogen is produced by the corpus luteum itself but doesn't maintain it. Progesterone is a product of the corpus luteum, not the maintaining factor. Another possible wrong option could be prolactin, which is involved in lactation, not directly in corpus luteum maintenance.

The clinical pearl here is the role of hCG in pregnancy tests. Since hCG is produced by the placenta and maintains the corpus luteum, detecting hCG in urine or blood is the basis for early pregnancy diagnosis. Also, understanding that in non-pregnant cycles, the corpus luteum regresses after about 14 days, leading to menstruation.

I need to make sure that the correct answer is hCG (human chorionic gonadotropin), which is secreted by the placenta. The options might be labeled with different hormones, so the correct answer would be the one corresponding to hCG. The other options would be other hormones that don't have this role. The explanation should clearly state why hCG is the right answer and why the others are wrong. Also, the clinical pearl about pregnancy tests is a key takeaway.

**Core Concept**
The corpus luteum is a temporary endocrine structure that secretes progesterone to maintain the uterine lining. Its survival during early pregnancy depends on **human chorionic gonadotropin (hCG)** from the placenta, which mimics luteinizing hormone (LH) to prevent luteolysis.

**Why the Correct Answer is Right**
In pregnancy, the placenta produces **hCG**, which binds to LH receptors on the corpus luteum. This interaction sustains luteal function, ensuring continued progesterone secretion until the placenta can independently produce steroids (~10–12

✓ Correct Answer: B. LH