A 32-year-old woman, G4P2, presents to your office at 20 weeks gestation for her first prenatal visit. She conceived with a new partner, and pregnancy was unplanned. Her obstetric history is significant for Rh(D) alloimmunization that complicated her last pregnancy. Her partner’s Rhesus genotype is CDe/cde. On routine laboratory workup, her antibody titer is 1:32. Which of the following is the best next step in management?