For something to do in your free time, dig around the U.S Patent and Trademark Office, and take a boo through their database. Do you know what a trademark is? By registering a trademark, a company claims (and obtains) the exclusive legal right to use that word or phrase. A trademark is a brand name.
What is a trademark? By the USPTO FAQ, "Trademarks include any word, name, symbol, or device, or any combination, used, or intended to be used in commerce to identify and distinguish the goods of one manufacturer or seller from goods manufactured or sold by others, and "to indicate the source of the goods."
Why is this relevant? Because if you do a search on the USPTO trademark database, you will find that the term "birthmother" is the trademark of Birthmother Ministries, a group that focuses on convincing mothers to surrender babies for adoption. They befriend vulnerable mothers, steer them towards surrendering, and link them up with baby brokers who can then lovingly harvest them. Yes, folks, this means that they legally own that word. Interesting that, according to the definition of what a trademark is, it distinguishes indicates the source of the goods. Gee, the source of the goods -- all those little babies being brokered for adoption -- are the good ol', happily-surrendering, splayed-on-their-backs birthmothers, eh? Or, should we say, birthmothers™.
Interesting. You too can be a brand name owned by that company, a "source" of "goods." And not only that, but the very name does not belong to you, but to a company that "lovingly" separates mothers from their children. Mothers of adoption loss, this is just one more reason to question whether you really want to be labeled by this term. Never mind that, according to the letter of the law, technically you cannot use this term without their permission.