It could be her long - time boyfriend. They might have been planning for a family in the future, but the pregnancy comes as a bit of a surprise earlier than expected.
Yes, there might be some out there. You can try searching on fanfiction websites like Archive of Our Own. They have a large collection of various fanfictions, and it's possible to find ones related to Beetlejuice and Lydia in such a situation.
A new, unknown supernatural entity that feeds on the energy of unborn children with special powers. It senses the unique nature of Lydia and Parrish's baby and starts to haunt them. It causes all kinds of problems like making Lydia sick, or creating nightmares for Parrish, all in an attempt to get closer to the baby so it can feed on its energy.
The main characters are clearly Lydia and Aiden. Since it's a pregnant fanfiction, they are likely the couple who are going to experience the journey of pregnancy together.
In the fanfiction, it could be that the pregnancy is a turning point in their lives. Lydia and Aiden could be part of a fantastical world where the pregnancy has some special meaning or power. For example, the baby could be prophesied to bring great change to their world. So they not only have to deal with the normal aspects of pregnancy like doctor visits and baby showers, but also protect the unborn child from those who might want to use its power for evil.
In a Beetlejuice and Lydia pregnant fanfiction, it could start with a big shock for both of them. Beetlejuice, who is used to his carefree and chaotic life, would suddenly be faced with the idea of impending fatherhood. He might initially be in denial or overreact in his typical Beetlejuice fashion. Lydia, on the other hand, would have to balance her normal life with this new situation. There could be a lot of comical moments as Beetlejuice tries to understand pregnancy, like thinking he can use his spooky powers to make it easier. And as the pregnancy progresses, they would face challenges together, such as dealing with the reactions of Lydia's family and friends who might not understand her relationship with Beetlejuice. Also, the supernatural elements could come into play, like the baby having some sort of special powers or a connection to the afterlife that they have to figure out how to handle.
It would likely become more intense. They'd have a deeper bond due to the shared responsibility of the baby. Scott would probably be more affectionate and caring towards Lydia.
Perhaps in the fanfiction, Lydia is pregnant in a post - apocalyptic world. She has to find ways to protect herself and her unborn baby from various threats. This could involve teaming up with unexpected allies and facing difficult moral choices along the way.
Their relationship would transform in many ways. They'd have to start thinking as a unit, not just as individuals. Stiles would become more responsible and Lydia would see a new side of him. She, in turn, would become more vulnerable in front of him, sharing her insecurities about motherhood. There would be a deeper level of trust as they share the journey of pregnancy. They'd also start to plan their future more concretely, which would involve a lot of compromise and understanding, thus changing their relationship dynamics for the better.
Perhaps they find out they're pregnant unexpectedly. Stiles starts making all these plans for their future as a family right away. Lydia is more cautious, thinking about how this will change their lives completely. Their friends could also play a big role, some being super supportive while others might be skeptical. And they could have to deal with family reactions, like Stiles' dad being really excited and Lydia's parents having mixed feelings.