Which of the following is not an important step in lactation ?

Options

A. Prolactin levels increase steadily during pregnancy.
B. Estrogens and progesterone stimulate the growth and development of breasts throughout pregnancy.
C. High prolactin level induces milk accumulation during pregnancy .
D. After parturition, estrogen and progesterone level decreases and lactation occurs

Answer

To determine which of the following statements is not an important step in lactation, we need to analyze each option related to the lactation process.

### Step-by-Step Solution:

1. **Understanding Lactation**:
- Lactation is the process of milk secretion from the mammary glands in mammals, primarily occurring during pregnancy and after childbirth (parturition).

2. **Analyzing the Options**:
- **Option 1**: "Prolactin levels increase steadily during pregnancy."
- This statement is true. Prolactin is a hormone that promotes milk production, and its levels do increase during pregnancy to prepare the body for lactation.

- **Option 2**: "Estrogens and progesterone stimulate the growth and development of breast throughout the pregnancy."
- This statement is also true. Estrogens and progesterone are crucial for the development of breast tissue during pregnancy.

- **Option 3**: "High prolactin level induces milk accumulation during pregnancy."
- This statement is misleading. While prolactin is responsible for milk production, it does not induce milk accumulation during pregnancy. Instead, milk accumulation primarily occurs after childbirth when the hormonal environment changes.

- **Option 4**: "After parturition, estrogen and progesterone levels decrease and lactation starts."
- This statement is true. After childbirth, the levels of estrogen and progesterone drop, allowing prolactin and oxytocin to take over and initiate lactation.

3. **Identifying the Incorrect Statement**:
- The third statement is the only one that is incorrect regarding the lactation process, as it inaccurately describes the role of prolactin in milk accumulation during pregnancy.

### Conclusion:
The correct answer to the question "Which of the following is not an important step in lactation?" is **Option 3: "High prolactin level induces milk accumulation during pregnancy."**