Ok..this might get complicated, but ill try and make it simple.

in terms of blood group, you can be A, B, AB, or O. and then you can be either a + or - of any of these. In a majority of cases, in pg only the + and - factor affect babies and mums.
I'll just talk about + and - for simplicity.

basically + means you HAVE the RH factor D antigen, and - means you DONT have the RH factor D antigen (on the surface of your red blood cells)

if your body recognises an antigen your ok, but if you get an antigen in your body your body does not know, it will make an antibody to fight and kill it.

so in terms of mums who are - means they don't have the antigen. when pg, they expect about a 6ml blood transfer from BUB to MUM (obviously mum to bub is alot more because of the placenta and growth etc). sometimes there is a little more blood going from baby to mum, esp. if mum gets hurt and there is trauma.

so, say mum is - and baby is + (this means baby HAS the antigen, but mum does not) and if a little bit of babies blood goes into mums, all of a sudden this antigen is in mums blood system, and her immune system will see it as a threat (because it hasnt seen it before), so mums immune system makes a antibody and tries to kill all the + things in mums body....including the sourse, her baby.

so to prevent mums immune system from destroying her baby, we give mums 'anti D' so her body recognises it earlier and doesnt build an antibody.

does that make sense?

and in terms of if mums + what are the chances of bub being + and -....ill try and draw a table.

look at it like everyone has 2 things. like if you are + you are either ++ ( 2 postives) or + - (one positive and one neg). to be - you have to be - - (two negs.)

so if mum is ++, and dad is ++ then baby is deff a ++.
if mum is ++ and dad is + - then baby will still be + because even if dads - bit is passed on, it would still be + - and therefore +


you can get a - baby if both parents are -. but you can also get a - baby if one parent is - and one parent is + (if the are a + -)

I tried drawing a table...but looked away to messy


but i hope this helps people!!