All interventions are technically optional as they can't do anything to you without your consent but you will need to check with the hospital policy. The hospital I attended (a low risk facility), was their policy to give the injection and if you were going to refuse it (obviously before the baby is born)they wouldn't let you deliver there. Having said that, the injection wasn't given to me immediately so my daughter was given the benefit of the extra blood first. You need to do what is right for you so make sure you are informed. I was anti injection initially and only wanted it if I started to haemmorrhage, but then it was explained to me that it may be too late then and the injection won't necessarily stop a haemmorrhage that has already started, which made perfect sense to me as prevention is better than cure, so I went with it. In all honesty, I didn't care what they did to me after my DD was born as I was so amazed at her. The prevention is better than cure thing works for me as I have a medical background and that is how I would manage all of my patients so it made sense to me. Good luck with your decision but defintely check out the policy of the hospital, although it sounds like you can decline it otherwise they wouldn't have asked.