My bump is fine, it's just his measurements on his tummy that are a week ahead. No one is really worried - we're more doing the sugar test 'just in case'. For that I'm feeling quite relaxed. 
Rhc negative is to do with blood type. Most folks are positive but it seems some of us are negative... if the mum is negative, as is my case then the key matter is if the baby is also, or if they're positive. this we don't know until after birth...
So, if a baby is positive then the mother will at some point start producing antibodies to fight off the Rhc positive antigens (I think that's what they're called). This usually happens after birth when some of the baby's blood enters the mothers blood stream. No risk to baby but it is a serious issue to future pregnancies as it can cause miscarriage, brain damage etc etc. So they give new mum's an injection within hours of the birth to stop the production of the antibodies. All good there...
The issue becomes if for some reason baby's blood enters my blood stream BEFORE birth. If that happens then I start producing antibodies whilst pregnant which can then enter the placenta and attack the baby. You can see where this is going... what the treatment is then I don't yet know, although I think I'd be well known at the hospital!
However, that is incredibly unlikely and only an issue IF the baby is Rhc positive... he could just as easily be Rhc negative in which case problem solved.
So right now we have a lot of unknowns, but thankfully I'm in incredible care and being well looked after. Just a little peeved as I thought this was meant to just happen without issue and end up with a bouncy baby boy in a few months!
Sorry, long post again but no easy way to explain otherwise.