**Core Concept**
Fluoride exposure during pregnancy can have both beneficial and adverse effects on the developing fetus. The primary concern is the potential for excessive fluoride intake to cause dental fluorosis, skeletal fluorosis, and even developmental delays in the child.

**Why the Correct Answer is Right**
Fluoride crosses the placental barrier and can accumulate in the fetus's bones, teeth, and other tissues. However, the recommended daily intake of fluoride for pregnant women is 3-4 mg/day, which is generally considered safe. This is because fluoride helps prevent tooth decay and promotes healthy bone growth. Nevertheless, excessive fluoride exposure can lead to an increased risk of dental fluorosis, a condition characterized by white or brown spots on the teeth.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because fluoride exposure during pregnancy has been shown to have both beneficial and adverse effects on the developing fetus. While excessive fluoride intake can cause dental fluorosis, the recommended daily intake is generally considered safe.
* **Option B:** This option is incorrect because fluoride does not have a direct toxic effect on the fetal brain. However, high levels of fluoride exposure have been linked to an increased risk of developmental delays and reduced IQ in children.
* **Option C:** This option is incorrect because fluoride exposure during pregnancy can lead to an increased risk of dental fluorosis, a condition characterized by white or brown spots on the teeth.

**Clinical Pearl / High-Yield Fact**
The optimal concentration of fluoride in drinking water is between 0.7 and 1.2 mg/L, as this range is associated with the lowest risk of dental fluorosis and the highest benefits for oral health.

**Correct Answer:** A.