**Core Concept**
Systemic Lupus Erythematosus (SLE) is a chronic autoimmune disease that can affect multiple organs, including the skin, joints, kidneys, brain, and other tissues. Managing SLE in pregnancy requires careful consideration of the medication's safety profile for both the mother and the fetus.

**Why the Correct Answer is Right**
In pregnant women with SLE, the primary goal is to control the disease while minimizing fetal risks. Corticosteroids, such as prednisone, are commonly used to manage SLE symptoms and are generally safe during pregnancy. Hydroxychloroquine is another key medication for SLE that has been shown to be safe and effective in pregnant women. Azathioprine is a purine synthesis inhibitor that can be used in pregnancy, particularly for women with lupus nephritis. However, certain medications like **Option C: Cyclophosphamide** are contraindicated in pregnancy due to their teratogenic effects and the risk of fetal harm.

**Why Each Wrong Option is Incorrect**
**Option A:** Corticosteroids are commonly used in pregnancy for SLE management.
**Option B:** Hydroxychloroquine is a safe and effective medication for SLE in pregnant women.
**Option D:** Azathioprine can be used in pregnancy, especially for women with lupus nephritis.

**Clinical Pearl / High-Yield Fact**
When managing SLE in pregnancy, it's essential to weigh the benefits and risks of each medication and consider the individual patient's disease activity and medical history.

**Correct Answer:** C. Cyclophosphamide. Cyclophosphamide is contraindicated in pregnancy due to its teratogenic effects and the risk of fetal harm.