Natural Mother vs Birth Mother vs First Mother vs Biological Mother

I noticed the near consistent use of the term Natural Mother on this website as opposed to any of its alternatives. I am familiar with the opposition against the term Birth Mother as put forth in this quote:

Birthmother" is a dehumanizing and coercive term, which makes a mother appear as if she was only the source of a baby for adoption, not her child's mother and parent. Instead of "birthmothers", "birthparents" (aka "birth objects") the honest terms "mother", "father" and "parents" should be used. If necessary, mothers whose children have been adopted-out may be called "natural mothers" to distinguish them from the people who adopted their children.

taken from keepyourbaby.com

Does any of the members know the history of these terms and the rational behind each choice?