My daughter started transfusion at 3 months age. the ideal pre transfusion HgB is between 9.5 and 10.5. if her HgB is between that range after 3 weeks, then that is the right interval for transfusion in my opinion. At this age, the child is growing very quickly so her body probbaly needs this. we also had to start with every 3 week transfusion and then settled for every 4 weeks. But now again, it looks like we have to change back to every 3 weeks.