A 32-year-old woman with a history of two previous pregnancies (both delivered vaginally without complications) presents to the antenatal clinic at 28 weeks gestation. Her blood group is O Rh-negative. Routine antenatal serum screening shows an indirect Coombs test (IAT) positive with an anti-D titre of 1:16. Ultrasound shows no evidence of fetal hydrops. What is the most appropriate next step in management?