Why are his mother and father referred to as his bio-mom and bio-dad?

In North America, there are a variety of mixed families.  There are many children whose biological parents are no longer together.  This means that a child may live with his biological mother but a step father, or his biological father and a step mother.  Another possibility is that the child is being raised by a single parent.  Medical staff will identify the child’s caregivers according to their blood or marital relationship with that child.