What may be a more interesting twist is if Ana is the one who is pregnant, because more likely than not, it's Aaron's baby. Aaron's love life is rocky at best given that he lusts after every woman who speaks to him. He falls for Zoey after she gives up on him, he's friends with benefits with Ana and debates whether or not he can be in a relationship with her, and now he believes Zoey is his person again.
What's important to remember is the time Aaron and Ana do spend together. Their connection seems genuine, and despite their differing political views, they come together to have open conversations, developing something real and respectful. They also have a lot of sex, so that part checks out.