**Core Concept**
In pregnancy, particularly in the second and third trimesters, insulin resistance increases due to placental hormones. Therefore, the antidiabetic drug of choice should be safe for both mother and fetus, minimize the risk of hypoglycemia, and effectively manage blood glucose levels.

**Why the Correct Answer is Right**
The drug of choice in pregnancy-induced hyperglycemia is insulin. Insulin is the most effective and safest option for managing blood glucose levels, as it directly lowers blood glucose levels and does not cross the placenta in significant amounts. This reduces the risk of hypoglycemia in the fetus. Metformin, another option, is not typically used in pregnancy due to its association with birth defects and potential for fetal growth restriction.

**Why Each Wrong Option is Incorrect**
**Option A:** Glyburide is a sulfonylurea that can cross the placenta and increase the risk of fetal hypoglycemia and other complications.
**Option B:** Metformin is generally avoided in pregnancy due to its association with birth defects and potential for fetal growth restriction.
**Option C:** Pioglitazone is a thiazolidinedione that can increase the risk of fetal heart defects and other complications.

**Clinical Pearl / High-Yield Fact**
In pregnancy, the American College of Obstetricians and Gynecologists (ACOG) recommends using insulin as the first-line treatment for gestational diabetes mellitus (GDM).

**Correct Answer:** C. Insulin.