**Core Concept**
Hypothyroidism in pregnancy is a condition where the thyroid gland does not produce enough thyroid hormones, leading to a decrease in the metabolic rate of the mother and the fetus. This condition can have significant effects on fetal development and maternal health.

**Why the Correct Answer is Right**
The correct answer is related to the pathophysiology of hypothyroidism in pregnancy. During pregnancy, the thyroid gland's demand increases to support the growing fetus. If the mother has hypothyroidism, it can lead to decreased levels of thyroid hormones, including triiodothyronine (T3) and thyroxine (T4). This decrease in thyroid hormones can affect the fetal brain, leading to cretinism, a condition characterized by severe intellectual disability and physical abnormalities. Additionally, hypothyroidism in pregnancy is associated with an increased risk of miscarriage, preterm labor, and preeclampsia.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not accurately describe the effects of hypothyroidism in pregnancy. While hypothyroidism can lead to weight gain, it is not the primary concern in pregnancy.
**Option B:** This option is incorrect because it is a treatment for hypothyroidism, not a consequence of the condition in pregnancy.
**Option C:** This option is incorrect because it is a consequence of hyperthyroidism, not hypothyroidism, in pregnancy.

**Clinical Pearl / High-Yield Fact**
It is essential to diagnose and manage hypothyroidism in pregnancy promptly to prevent adverse effects on fetal development and maternal health. TSH levels should be monitored regularly, and thyroid hormone replacement should be initiated if necessary.

**Correct Answer:** C.