A 26-year-old woman with bipolar I disorder has been stable on valproic acid 1000 mg daily for 2 years. She presents to the clinic reporting that she and her partner are considering pregnancy within the next year. Her most recent labs show a valproic acid level of 85 mcg/mL, AST 28, ALT 32, CBC within normal limits, and a negative pregnancy test. Which of the following is the most important counseling and management consideration?