**Core Concept**
Congenital adrenal hyperplasia (CAH) is a group of inherited disorders that affect the adrenal glands, leading to impaired production of cortisol and aldosterone. In fetal CAH, the deficiency of 21-hydroxylase enzyme causes an accumulation of 17-hydroxyprogesterone, resulting in excessive androgen production. This can lead to virilization of female fetuses. Maternal treatment with glucocorticoids is essential to prevent virilization.

**Why the Correct Answer is Right**
Dexamethasone is the preferred glucocorticoid for the treatment of CAH in pregnant females due to its ability to cross the placenta and effectively suppress fetal adrenal androgen production. **Dexamethasone has a longer half-life and higher potency than other glucocorticoids**, allowing for less frequent dosing and more effective fetal treatment. Additionally, dexamethasone's minimal mineralocorticoid activity reduces the risk of maternal hypertension and hypokalemia.

**Why Each Wrong Option is Incorrect**
**Option B:** Betamethasone is a glucocorticoid used for fetal lung maturation in cases of preterm labor, but it is not the preferred agent for CAH due to its shorter half-life and lower potency compared to dexamethasone.

**Option C:** Hydrocortisone is a glucocorticoid with both corticosteroid and mineralocorticoid activity, making it less ideal for CAH treatment in pregnant females due to the risk of maternal hypertension and hypokalemia.

**Option D:** Prednisolone is a glucocorticoid with significant mineralocorticoid activity, which would increase the risk of maternal hypertension and hypokalemia in CAH treatment.

**Clinical Pearl / High-Yield Fact**
To prevent fetal virilization, maternal treatment with dexamethasone should be initiated as early as possible in the pregnancy, ideally between 9 and 16 weeks of gestation. Regular monitoring of fetal development and maternal side effects is crucial to ensure effective treatment and minimize risks.

**✓ Correct Answer: A. Dexamethasone**