A 28-year-old primigravida with Rh-negative blood group presents at 34 weeks of gestation with a history of vaginal bleeding following minor trauma. On examination, she is haemodynamically stable. The indirect Coombs test (ICT) is positive with an antibody titre of 1:16. Ultrasound shows a live singleton fetus with normal liquor volume. What is the most appropriate next step in management?