I would say go to outpatient at the hospital and say you need Rhogam... here you have to go to the hosptial if you have a home birth with a midwife (with my first few births the mw could give it, but I'm in a different state now).
You could just go in and say you had baby at home and need the shot... taking baby with you. Or you could go w/o baby if you're worried. You need to tell them you had a baby and not a m/c b/c the dosages are different.
I agree with the Eldon card - it can help you type baby's blood after birth. If you are seeing a care provider you could possibly also ask for a new screening that will tell you baby's blood type before birth (it is a blood test done on Mom - non-invasive for the baby). I interviewed the doctor who developed the test here:Rh Genotyping
That would let you know what baby is now.
I would like to UC with our next babe (last babe was an accidental UC and he was Rh Negative so we didn't even need to worry about the hosptial).
Good luck as you decide what to do. I have always opted for the postpartum shot if my babies were Postive and will try to arrange it for a UC, too.