**Core Concept**
Ebstein anomaly is a congenital heart defect characterized by an abnormal formation of the tricuspid valve and right ventricle. This condition is associated with various teratogenic effects, particularly in the context of maternal lithium exposure during pregnancy.

**Why the Correct Answer is Right**
Lithium, a medication commonly used to treat bipolar disorder, has been linked to Ebstein anomaly in several epidemiological studies. The exact mechanism of lithium-induced Ebstein anomaly is unclear, but it is thought to involve disruptions in fetal cardiac development, particularly during the first trimester of pregnancy. Lithium may interfere with the normal functioning of the cardiac neural crest cells, which are crucial for the proper formation of the tricuspid valve and right ventricle.

**Why Each Wrong Option is Incorrect**
**Option A:** Clozapine is an atypical antipsychotic medication that is not typically associated with Ebstein anomaly or other congenital heart defects. Its primary teratogenic effects are related to weight gain and metabolic disturbances.

**Option B:** Phenytoin is an antiepileptic medication that has been linked to various congenital anomalies, including cleft palate and heart defects. However, its association with Ebstein anomaly is not well established.

**Option D:** Lamotrigine is another antiepileptic medication that has a relatively favorable safety profile during pregnancy. While it may be associated with some congenital anomalies, Ebstein anomaly is not a commonly reported effect.

**Clinical Pearl / High-Yield Fact**
It is essential for healthcare providers to carefully weigh the benefits and risks of lithium treatment in pregnant women, particularly during the first trimester. Close monitoring and alternative treatment options should be considered to minimize the risk of Ebstein anomaly and other potential teratogenic effects.

**✓ Correct Answer: C. Lithium**