FULL ANSWER Human blood factors are grouped as A, B, AB
and O, which are important to know for the
purposes of transfusions and transplants. In
addition to these factors, the blood is also
described as Rh-positive or negative. As
explained by, the Rh factor has no effect on human health except during
pregnancy. Around 15 percent of the general population is
Rh-negative. When an Rh-negative mother
conceives a child with an Rh-positive father,
the mother’s immune system sometimes
becomes sensitized and begins to produce
antibodies that cross the placenta and damage the fetus’ red blood cells. This hemolytic
disease, as describes, can cause
anemia, brain damage and death. This danger
makes it all the more important to seek
adequate medical care during pregnancy and,
since the danger increases with subsequent pregnancies, always provide a full and
accurate medical history to the doctor.

Source: Tuorimuo Elvis Philip/Upper West Media.