There could be many interesting fanfics on this topic. Maybe it would explore how Betty deals with the pregnancy in the complex world of Riverdale, like how her friends and family react. Archie might be shocked and Jughead could be there to support her in a really unexpected way.
Maybe Betty gets pregnant and it causes a rift between her and Jughead. Jughead is really focused on his writing and his own future and he's not sure if he's ready to be a father. This could lead to a lot of drama and emotional turmoil as Betty tries to convince him that they can make it work and that she needs his support.
Jughead is often involved. Since he and Betty have a complex relationship in the show, in fanfiction about her pregnancy, he could be the father, and they would have to deal with the implications of that. Veronica is also a common character. She might be Betty's confidante, helping her through the pregnancy, or there could be some jealousy or conflict if Jughead is the father. Archie could also be involved, perhaps as a supportive friend or in a more complicated love triangle - type situation.
Perhaps Betty's pregnancy could be a part of a bigger mystery in Riverdale. It could be related to some dark secret in the town. For example, there could be a group that is targeting pregnant women in the town, and Betty has to figure out how to protect herself and her unborn child while also dealing with the normal pregnancy - related issues like morning sickness and doctor's appointments.
Physically, you can show Betty with dark circles under her eyes, constantly yawning, and her movements being sluggish. For example, when she's walking to school, she might be dragging her feet. Emotionally, she could be short - tempered with her friends and family, snapping at them easily because she's so tired of dealing with everything. You could also have her make mistakes she wouldn't normally make, like misplacing important evidence in a mystery she's solving.
One popular storyline could be Betty dealing with the unexpected pregnancy while also trying to keep up with the mysteries in Riverdale. For example, she might be hiding her pregnancy from some of the more dangerous characters in town as she tries to figure out who her real friends are. Another could be her pregnancy in the context of her relationship with Jughead, and how they navigate the challenges together, like financial concerns and family reactions.
One idea could be that Betty has been overworking herself on a big mystery in Riverdale. She's constantly chasing leads, staying up all night, and it's starting to take a toll on her. Maybe she starts having hallucinations related to the mystery, like seeing suspects everywhere she goes. Another plot could involve Betty being tired of the constant drama in Riverdale. She decides to take a break from all the chaos and goes on a solo trip outside of town, but of course, trouble follows her.
Some fanfictions might focus on the emotional journey of Jughead and Betty. They could be scared at first but then grow closer as they anticipate the arrival of their child. They might start to think about their future together more seriously. They could also face pressure from their friends, like Archie might have some concerns or Veronica could offer her own brand of support. In some plots, they may even consider moving away from Riverdale to start a fresh life for their family.
One popular plot could be how they deal with the unexpected pregnancy while still in high school. They might face judgment from their friends and family. For example, Betty's parents might be disappointed at first but then come around to support her. Another plot could involve their future plans. Maybe Jughead has to put his writing career on hold to support the family, or they consider moving out of Riverdale to start fresh.
It could also be a plot device to introduce a supernatural element. For example, she could be put into a magical sleep by a villain, and the rest of the story could revolve around her friends trying to wake her up, encountering various challenges and mysteries along the way.