Hemolytic disease of newborn and breastmilk

Aside from prematurity, ABO blood incompatibilty may also cause jaundice. My younger sister was born with orange color skin. She had exchange transfusion few days after she was born. My mom's blood type is O+, while my sister's blood type is B+. Oops, I forgot to tell this to my fairy godfather.

My blood type is O+,  my husband's is A+.  Then, what? I wish to have a very good neonatologist. Can I perform a Coomb's test from the cord blood? Will there be enough blood left for the cord blood banking?

Antibodies do not cross placenta, but how did my sister get HDN ? My mom did not breastfeed us. Btw, i always hear colostrum is very good for the babies. It contains antibodies for immune protection. Ei, does it contain antibodies to blood type a antigen?  I am afraid of antibodies.

Oops, Im just guessing about the reason for my sister's severe jaundice. Btw, my younger brothers is also blood tupe B+.