This is the sort of question highlighted in this BBC story about a 24-year-old Kenyan woman, Miss K, who refused a transfusion in Ireland. However, the hospital refused her refusal, sedated her and gave her blood. Now, the Republic's High Court has ruled that the medics were right to do as they did, and that Miss K's rights were not breached by their doing so.
In K's case, she was suffering a massive haemorrhage after having a baby (at Dublin's Women's Hospital last September). Her baby would, we hope, continue to live if she had died. But does she have a right to deprive the sprog of its mum? OK, she's a mum it wouldn't have remembered, but it would have faced a life among peers who did have mums. You may consider that is not reason enough to deny the woman the right effectively to end her own life. After all, we feel that people have a right to commit suicide, even though there will be people left behind to grieve and try to cope without their loved one.
The same BBC report touches on another story it carried in more detail earlier of anaemic twins due to be born to a pair of Jehovah's Witnesses who don't want their offspring to have the transfusions they will need within minutes of their birth and subsequently. The case here is clear, a no-brainer, you might say. No parent has the right to allow the kids to die because of their religions beliefs, their political beliefs or any other beliefs.
See a similar story we carried on 8 April, posing similar questions. See also why Jehovah's Witnesses don't like blood transfusions.