Zahra,
It did happen with our daughter too,she was on 4 weeks and then suddenly she started going on 3 weeks continuously,but then we started giving her Carao,and now her transfusion interval is almost always 4 weeks,so Carao,and i would like to think collectively all supplements do help with this,like Magnesium and folic acid helps with formation and strength of RBCs,wheat grass also helps,and i am not sure but i think the less free radicals in the blood the lesser the damage to the RBCs,so IP6 would help too,i don't have a medical proof for that but thats what i think.
Hope this helps,
Zaini.