This show would obviously not have a problem with the highly-unlikely nature of a woman Alexis's age being pregnant, but we'd have to have paternity questions added to the mix just to make it worth the effort. Obviously Dominique would go into core meltdown at the prospect of Alexis cementing her grip on Jeff's fortune with an heir, but if she found out Alexis had been sleeping around....
The tabloid-ish nature of such a story might get an extra points if Alexis's affair was with Blake, since it would be pretty obvious who the father is when the baby is born. There might be two points if Cristal becomes pregnant again at the same time and Blake is sweating out the prospect of having two baby-mamas at the same time.