My latest piece for What Culture lists 8 examples of television sitcoms that had an episode where a baby was born on an elevator. Truth be told, it has happened more than eight times. I did the research. The heart of the issue here is not silliness of the circumstances that lead pregnant women in TV world to get stuck on elevators moment before birth, but the complete lack of originality of writing in the entertainment industry. I say the entertainment industry, and not just television because it happens in movies, too... the recycling of old ideas. How many reboots and sequels are being produced right now? I have no idea, but it seems like a lot. Sam Raimi's Spiderman trilogy made have ended poorly, but who really wanted a reboot so soon? Chris Nolan's Dark Knight trilogy became the definitive Batman for at least a generation, but there's still talks of another reboot.
I can't think of any examples at the moment, but I don't doubt that the same thing happens in fiction writing. Given the explosion of self-publishing—and even without it—the market is supersaturated with content. Even if everyone's ideas were conceived individually, and without prior literary influence, there will be storylines that are similar.
When I conceived the idea of my novel, I actually made an attempt to determine if the idea had been done before. I'm fairly confident that it has not. If the plot idea had been done before, in largely the same way, I'd have likely scrapped the whole thing and come up with a new idea. I want to tell my own story and not rely on old, overused plotlines and gags in an attempt to gain interest. I wonder why television writers don't feel the same way?