Hello, Blood transfusion can be and should be given to your wife in the present condition as she is carrying a twin pregnancy. The usual precautions should be taken and the blood transfusion performed as a slow process to prevent undue load on the heart and also to help tackle any untoward effects. Minor side effects like headache, fever and itching or rash are possible while severe side effects include severe headache, breathing difficulty and abrupt changes in the blood pressure. These are observed with any transfusion and provided proper precautions are taken, transfusion is as safe as in the non-pregnant condition. Hope this helps.