A 32-year-old G2P1 Rh-negative woman presents at 36 weeks of gestation with a history of delivery of an Rh-positive baby 3 years ago. She did not receive anti-D prophylaxis after her first delivery. Current antenatal investigations show: Indirect Coombs test (ICT) positive at 1:16 dilution, hemoglobin 9.2 g/dL, and ultrasound shows mild polyhydramnios with normal fetal biometry. What is the most appropriate next step in management?