Select the correct option describing gonadotropin activity in a normal pregnant female.

Options

A. (a) High level of hCG stimulates the thickening of endometrium
B. (b) High level of FSH and LH stimulates the thickening of endometrium
C. (c) High level of FSH and LH facilitate implantation of the embryo
D. (d) High level of hCG stimulates the synthesis of estrogen and progesterone

Explanation

**Step-by-Step Solution:**

1. **Understanding Gonadotropins**: Gonadotropins are hormones that play a crucial role in regulating reproductive processes. In pregnant females, the primary gonadotropin of interest is human chorionic gonadotropin (hCG).

2. **Role of hCG**: Human chorionic gonadotropin (hCG) is produced by the cells surrounding the embryo shortly after implantation. It is essential for maintaining pregnancy.

3. **Effects of hCG**:
- hCG stimulates the synthesis of progesterone, which is vital for maintaining the uterine lining and supporting the embryo.
- It also promotes the synthesis of estrogen, which is necessary for normal pregnancy.

4. **Importance of Progesterone**: Progesterone is often referred to as the "pregnancy hormone" because it helps prepare the endometrium (the lining of the uterus) for the implantation of the embryo and supports its growth.

5. **Evaluating the Options**:
- **Option A**: "High-developed hCG stimulates the thickening of endometrium." - This is partially correct but misleading because hCG does not directly stimulate thickening; it stimulates progesterone, which does.
- **Option B**: "High level of FSH and LH stimulate the thickening of endometrium." - This is incorrect; progesterone is responsible for this action.
- **Option C**: "High level of FSH and LH facilitate the implantation of the embryo." - This is also incorrect; implantation is facilitated by progesterone.
- **Option D**: "High level of hCG stimulates the synthesis of estrogen and progesterone." - This is correct as hCG directly stimulates the production of these hormones.

6. **Conclusion**: Based on the analysis of the options, the correct answer is **Option D**.

---