**Core Concept**
The management of thyrotoxicosis in pregnancy requires careful consideration of the treatment options to ensure the safety of both the mother and the fetus. In a pregnant woman with thyrotoxicosis, the primary goal is to control the maternal thyroid hormone levels while minimizing the risk of fetal hypothyroidism and other complications.

**Why the Correct Answer is Right**
Beta-blockers, such as propranolol, are commonly used in the management of thyrotoxicosis in pregnancy to control the symptoms of hyperthyroidism, such as palpitations and tremors. However, the use of radioactive iodine (RAI) is contraindicated in pregnancy due to the risk of fetal thyroid ablation and subsequent hypothyroidism. This is because RAI can cross the placenta and cause damage to the fetal thyroid gland, leading to permanent hypothyroidism.

**Why Each Wrong Option is Incorrect**
**Option A:** Methimazole is an antithyroid medication that can be used in pregnancy to treat thyrotoxicosis, but it carries a risk of congenital abnormalities, such as aplasia cutis and esophageal atresia. While it is not an absolute contraindication, it is not the correct answer in this case.
**Option B:** Iodine is often used in the treatment of thyrotoxicosis, particularly in the form of Lugol's solution. It is safe to use in pregnancy and can help to reduce the vascularity of the thyroid gland, making it less likely to rupture.
**Option C:** Propylthiouracil (PTU) is another antithyroid medication that can be used in pregnancy to treat thyrotoxicosis. It is often used in the first trimester due to its lower risk of congenital abnormalities compared to methimazole.

**Clinical Pearl / High-Yield Fact**
Radioactive iodine should be avoided in pregnancy due to the risk of fetal thyroid ablation and subsequent hypothyroidism. If a pregnant woman requires treatment for thyrotoxicosis, antithyroid medications such as methimazole or PTU may be used, but with careful monitoring and consideration of the risks and benefits.

**Correct Answer:** C.