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Rh factor or rhesus factor is a type of antigen present in red blood cells in around 85% of total population. It doesn't affect the health of person as such, but during pregnancy woman is at risk if she is Rh negative and her partner is Rh positive as this combination will produce a child who is Rh positive. While the mother's and baby's blood systems are separated but there are times when from baby can enter mother blood leading to formation of antibodies against Rh factor which is fatal at times. 

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ty!! :)
wht r u doing nw
I mean which class ???
me in 12th.. and u