A 24-year-old female presents with severe, recalcitrant acne that has persisted for five years. She reports painful cystic lesions predominantly on her face, chest, and back, which have left deep, atrophic scars. Her acne significantly affects her self-esteem and has led to social withdrawal and mild depressive symptoms. She has tried multiple treatments, including topical retinoids, benzoyl peroxide, salicylic acid, and oral antibiotics (minocycline), with minimal success. She also attempted hormonal therapy with combined oral contraceptives but discontinued after experiencing side effects, including nausea and headaches. Frustrated with the lack of improvement, she seeks more definitive treatment. She is sexually active and uses condoms inconsistently for contraception. She is being initiated on isotretinoin at 0.5 mg/kg/day. What is the most critical precaution when prescribing isotretinoin to a female patient of childbearing age?
