Fact: A thing that is indisputably the case.
Fiction: Literature in the form of prose, especially short stories and novels, that describes imaginary events and people.
Nearly everyone loves movies. I have this friend who goes to the theater weekly, sometimes more, depending on what’s new. And every Monday morning when I ask how he liked this latest movie there’s one comment he repeats more often than I can count: “It just wasn’t real. I mean, those things aren’t possible.” My usual response is, “Well, it’s a movie.” However, in many cases, his criticism may be legit.
If you’re writing science fiction, fantasy or futuristic realism, it’s your world to make of what you will. Anything you can imagine can be probable, but even then your readers (or viewers if you’re writing a movie script) will want some sort of explanation or reasoning why this fantastical thing is possible in this world. If you’re writing any other genre of fiction, a lot of your story will be based on fact. Birds have wings, fish can breath underwater, and human’s can’t without assistance.
I also think we writers may occasionally forget this one fundamental and essential thing. If you want your readers to be engaged, if you want them to care about your MC(s) enough to keep turning those pages, then you need to be sure they can connect with those characters. And to have a connection, the reader has to believe your characters are real; that this story could be happening right now.
Keep in mind too that reading a 300-page novel is an investment of the reader’s time, most likely more valuable to that reader than the money spent to purchase it.
Bottom line: You might want to think twice before you decide to have your male character turn up pregnant. Or, if you insist on going there, make sure you’ve done your research and have your explanations fully formed. And by all means, define your genre correctly. It’s a big disappointment and one you’ll want to gripe about when you think you purchased a fine red wine then sit down to a romantic dinner and realize what you really got was Welch’s Sparkling Red Grape.