**Core Concept**
Phenytoin is a teratogenic antiepileptic medication that can cause fetal hydantoin syndrome when used during pregnancy. The management of epilepsy during pregnancy requires balancing the risks of seizures to the mother and fetus against the risks of antiepileptic medications.

**Why the Correct Answer is Right**
In the case of a pregnant woman with epilepsy on phenytoin therapy, the goal is to minimize the risk of seizures while minimizing the teratogenic effects of the medication. Folic acid supplementation is essential to prevent neural tube defects, but it is not sufficient to manage epilepsy. The correct approach is to switch to a safer antiepileptic medication, such as lamotrigine or levetiracetam, which have a lower risk of teratogenicity. **Option C** is the most appropriate choice.

**Why Each Wrong Option is Incorrect**
**Option A:** Folic acid supplementation alone is not sufficient to manage epilepsy in a pregnant woman on phenytoin therapy.
**Option B:** Continuing phenytoin without any changes is not advisable due to its known teratogenic effects.
**Option D:** Adding another antiepileptic medication without switching to a safer option is not the best approach.

**Clinical Pearl / High-Yield Fact**
In managing epilepsy during pregnancy, it is essential to consider the teratogenic effects of antiepileptic medications and to switch to a safer option if possible.

**Correct Answer: C. Lamotrigine or levetiracetam can be used as safer alternatives.**