Yes, there are likely some fanfics out there with such a plot. Fanfic writers often explore different 'what - if' scenarios in the Vampire Diaries universe. They might be interested in the dynamic between Damon and Caroline in a situation where they are expecting a child, which could lead to a lot of interesting character development and new storylines.
Perhaps the pregnancy could be a sign of a greater prophecy in the Vampire Diaries fanfiction world. Caroline might be seen as a key figure in a new chapter of the supernatural world. Her pregnancy could bring about a new era where vampires, witches, and werewolves have to come together to protect her and the baby from an ancient evil that has awakened due to this new life on the way.
One possibility could be that Klaus, being his possessive self, tries to protect Caroline during her pregnancy. He might use his power and resources to keep her safe from all the threats in the Vampire Diaries world, like other vampires or werewolves who might see a pregnant Caroline as an easy target or a threat to their power dynamics.
The vampire community's reaction would be complex. Some vampires, especially those who are more progressive or have a soft spot for Caroline, might support her. They could see her pregnancy as a sign of new beginnings and a way to bridge the gap between different factions in the vampire world. However, the older and more conservative vampires would probably oppose it vehemently. They might see it as a threat to their long - established traditions and hierarchies, and would stop at nothing to prevent the birth of a child that could potentially change the balance of power in the vampire world.
One interesting plot twist could be that the father of Caroline's baby is a long - lost relative of an original vampire. This would bring in a whole new level of drama as different vampire factions might try to either protect or harm Caroline and her unborn child depending on their own motives.
You can try fanfic websites like Archive of Our Own (AO3). It has a vast collection of fanfictions, and you can search for 'Vampire Diaries Damon and Caroline pregnant' in the search bar. There's a good chance you'll find some relevant fanfics there.
One common plotline is the struggle with their relationship. Since Klaus is a complex and often villainous character in the show, there's a lot of drama around how they'll raise the child together. For example, Caroline might be worried about Klaus's violent tendencies influencing their baby.
If Caroline is pregnant in the fanfiction, Klaus might see this as an opportunity to claim her and the baby as his own. He has always had a soft spot for Caroline. His possessive nature could lead to him becoming overprotective, which Caroline may or may not like. It could cause a lot of tension between them as Caroline values her independence.
One idea could be that Caroline's pregnancy is a result of a magical mishap. Maybe a spell gone wrong in Mystic Falls. The baby could have special powers, like being able to sense vampires from a distance. This would bring a whole new set of challenges for Caroline and her friends as they try to protect the baby from the various threats in the vampire - filled world.
Well, a popular one is 'A Klaus and Caroline Love Story'. In this, the author really focuses on building their emotional connection. There's also 'Klaus's Pursuit of Caroline' which is all about how Klaus goes to great lengths to win Caroline over. And don't forget 'Caroline's New Beginning with Klaus' where they start a new chapter together, away from the usual Mystic Falls drama.