Which of the following statements is correct?

Options

A. Rh compatibility must be tested before pregnancy establishment and blood transfusion
B. Rh antibodies can cross placenta
C. At the time of 1st delivery some of `Rh^(+)` RBCs from the baby `(Rh^(+))` mix the mother's blood `(Rh^(-))` due to tear in placenta mother's blood for `Rh^(-)` antibodies
D. All

Answer

To determine which statement is correct regarding RH compatibility and its implications during pregnancy and blood transfusions, we will analyze the statements provided in the question step by step.

### Step-by-Step Solution:

1. **Understanding RH Factor**:
- The RH factor is a protein that can be present on the surface of red blood cells. Individuals who have this protein are considered RH positive (RH+), while those who do not are considered RH negative (RH-).

2. **Analyzing Option 1**:
- The statement claims that RH compatibility must be tested before pregnancy, establishment, and blood transfusion. This is indeed correct. Testing for RH compatibility is crucial to prevent complications during pregnancy, especially if the mother is RH- and the father is RH+.

3. **Complications in Pregnancy**:
- If an RH- mother carries an RH+ fetus, complications can arise during delivery. If there is a rupture of the placenta, fetal blood can enter the maternal circulation, leading to the mother developing antibodies against the RH antigen.

4. **Consequences of Antibody Formation**:
- Once the mother has developed these antibodies, they can cross the placenta in subsequent pregnancies, leading to a condition known as Erythroblastosis Fetalis, where the mother's antibodies attack the fetal red blood cells.

5. **Analyzing Blood Transfusion**:
- In blood transfusions, if an RH- person receives blood from an RH+ donor, the same immune response can occur, leading to clumping of red blood cells (hemolysis) due to the formation of antibodies against the RH antigen.

6. **Conclusion**:
- Based on the analysis, the correct statement is that RH compatibility must indeed be tested before pregnancy and blood transfusion to prevent serious complications.

### Final Answer:
- The correct statement is: **RH compatibility must be tested before pregnancy, establishment, and blood transfusion.**