Three women were brought to a hospital.........the X-factor of Development

Three women were brought to a hospital, each in the same condition and each needing a blood transfusion.
The first, a Black woman was given the transfusion but died a few hours later.
The second, a Hispanic woman was also given a transfusion but died a few days later.
The third, a White woman, was given a transfusion and survived.
That is the X factor in development.