I realise that, my connecting thought was that the hospital looking at their insurance policy should have been able to understand the pregnancy was covered. Even with it being unclear due to the contract's wording, it should have triggered the billing department contacting the insurer for clarification.

That's not how America works though, they operate on a 'invoice first, ask questions later' approach. If one in a thousand bills get paid without question, the superfluousness is considered justified. Oh well, I would add this to my list of reasons to avoid the country if it weren't so long already.