A 24-year-old woman undergoes routine evaluation. She is pregnant at 12 weeks' gestation. Medical history is notable for homozygous sickle cell anemia (Hb SS). She has had multiple uncomplicated painful crises treated at home with hydration, nonopioid analgesia, and incentive spirometry. She requires hospital management for these episodes approximately twice per year. She has declined the use of hydroxyurea. Her only other medication is folic acid.

On physical examination, vital signs are normal. Mild scleral icterus is noted. A grade 2/6 early systolic flow murmur is heard at the cardiac base. The examination is otherwise normal.

Laboratory results show a hemoglobin level of 7.5 g/dL (75 g/L).

Which of the following is the most appropriate management?