Hi. I'm a new user, but I hope my advice might help a bit. When I was pregnant years ago, I got rather depressed, although not to the extent that i'm reading here.
I can appreciate your wife not wanting to take some happy pill especially when she's pregnant.
Have you thought of going along on your wife's next visit to the gynocologist and telling the doctor what you've written here? If it seems more urgent, how about calling your wife's doctor right away and telling her of your concerns?
I wouldn't wait for someone who's depressed to take the initiative and call, often it's hard to get motivated to do anything in that condition.
Hope this helps.
Also, if you can get your work schedule changed so that you are with her more often, it couldn't hurt.