Is it safe to take phenytoin while pregnant or breastfeeding?

No: Phenytoin use during pregnancy has been associated with many fetal abnormalities including, head and facial abnormalities, brain abnormalities, and development delays. "fetal hydantoin syndrome" is a disorder in infants characterized by many of these abnormalities.

Not during pregnancy: This is a category d drug with known fetal toxicity. A syndrome of abnormalities is well known. It is considered relatively safe during breastfeeding.