A 28-year-old woman with bipolar II disorder, well-stabilized on lamotrigine 200 mg daily for three years, presents at 8 weeks gestation for psychiatric consultation. She has a history of severe depressive episodes with one prior psychiatric hospitalization, and lamotrigine was the only mood stabilizer that achieved sustained remission. Her obstetrician has confirmed a viable intrauterine pregnancy. The patient and her partner planned this pregnancy, and she wishes to continue lamotrigine given her high relapse risk. Her pre-pregnancy lamotrigine serum level was 7.2 mcg/mL. The PMHNP discusses the pharmacokinetic implications of pregnancy on lamotrigine therapy. Which of the following most accurately describes the rationale for lamotrigine dose adjustments during pregnancy?